Bishop 1997

8122019 Bishop 1997

httpslidepdfcomreaderfullbishop-1997 125

Cognitive Neuropsychology and

Developmental DisordersUncomfortable Bedfellows

DVM BishopMRC Applied Psychology Unit Cambridge UK

Cognitive neuropsychology provides a theoretical framework and methods that can be of value in the study of developmental disorders but the ``dissociationrsquorsquo logic at the centre of this approach is not well suited to the developmental context This is illustrated with ex-amples from speci c language impairment Within the developing language system there isample evidence for interaction between levels of representation with modularity emerging inthe course of development This means that one typically is seeking to explain a complexpattern of associated impairments rather than highly selective de cits For instance a select-ive impairment in auditory processing can have repercussions through the language systemand may lead to distinctive syntactic de cits that are seen in written as well as spoken

language Changes in the nature of representationsand in the relationshipsbetween compon-ents of a developing system mean that cross-sectional data at a single point in developmentmay be misleading indicators of the primary de cit Furthermore traditional cognitiveneuropsychology places a disproportionate emphasis on representational (competence) de-

cits with processing (performance) de cits being relatively neglected Methods for distin-guishing these two kinds of impairment are discussed as well as other approaches forelucidating the underlying nature of developmental disorders

Cognitive Neuropsychology Dissociated Deregcits andModularity

John Marshallrsquos EPS 50th Anniversary lecture described how the Experimental Psychol-ogy Society provided a stimulating forumfor interactions between cognitive psychologistsand neuropsychologists in the 1960s and 1970s leading to the owering of the disciplineof cognitive neuropsychology From the start the aim of the enterprise was to developand test models of the cognitive processes involved in particular mental operations by

THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY 1997 50A (4) 899 _ 923

This paper is based on an invited presentation to the Experimental Psychology Society in Cambridge July1996 in celebration of the 50th anniversary of the founding of the Experimental Psychology Group from whichthe Society subsequently evolved

Requests for reprints should be sent to DVM Bishop MRC Applied Psychology Unit 15 Chaucer RoadCambridge CB2 2EF UK Email dorothybishopmrc-apucamacuk

Thisarticle is based in part on chapter 9 in DVM Bishop Uncommon understanding development and disordersof language comprehension in children published by Psychology Press 1997

Oacute 1997 The Experimental Psychology Society

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analysing patterns of de cit in brain-damaged individuals (see Coltheart (1987) andShallice (1988) for reviews) The emphasis was largely on case studies that demonstratedhighly selective patterns of cognitive de cit and could inform theory by demonstratingthe relative independence of different cognitive processes A great deal of evidence has

accumulated to support the view that not only is language processing largely independentof other cognitive functions but within the language systemthere are independent stagesthat may be selectively disrupted For instance one may see patients who lose the abilityto understand spoken language while retaining the ability to repeat (eg Berndt Basili ampCaramazza 1987) or who are able to read content words but not function words (Gardneramp Zurif 1975) others may have particular dif culty in understanding sentences wherewordorder is critical (Schwartz Saffran amp Marin 1980) in yet other cases there may beloss of the ability to name or comprehend items of a given semantic class (eg Warringtonamp McCarthy 1987) Evidence such as this has been used to develop information proces-sing models of language comprehension as involving a sequence of repesentational stageseach largely independent of the other (eg Figure 1)

The publication of Fodorrsquos (1983) in uential book The Modularity of Mind incorpor-ated many of the ideas that had developed in cognitive neuropsychology by proposingthat much of our cognitive processing is modular According to Fodor a module is adomain-speci c and informationally encapsulated brain systemresponsible for handling aparticular type of mental representation which has the properties listed in Table 1 Thismay be illustrated by considering how the brain handles speech perception Domain

speci city refers to the fact that the mechanisms involved in speech perception appearto be distinct from those used for other kinds of auditory analysis and operate only onacoustic signals that are taken to be utterances Information encapsulation refers to thefact that modular processing cannot be in uenced by higher cognitive operations Thisresults in mandatory processing one cannot easily ignore incoming speechmdasheven if attention is switched away from interpreting utterances one will immediately respondon hearing a salient signal such as onersquos own name Processing in a modular systemis fastand automatic in contrast to central processes concerned with long-term memory andreasoning which are typically slow optional and general-purpose able to combine infor-mation froma variety of sources In Fodorrsquos scheme processing of language is modular upto the stage where a propositional representation is generated Later stages of under-standingmdashthat is incorporating general and social knowledge to interpret the utterancemdash are seen as involving central processes and do not have the characteristics of modules

Fodor used evolutionary arguments to support the idea that a complex processor thatrapidly performs a dedicated function (ie a module) is likely to be innately pre-pro-grammed and the nding that damage to a particular brain region can lead to a selectiveimpairment in a particular stage of language processing has been taken as evidence forthis

900 BISHOP

FIG 1 Information processing model showing the sequence of representations generated in comprehendingthe sentence ` the sh is on the tablersquorsquo Pragmatic in uences on interpretation (handled by Fodorrsquos so-called` central processesrsquo rsquo) are not shown and processing is depicted as entirely bottom-up

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901

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The claim that modules are innate is important because it implies that the logic of thecognitive neuropsychology approach can be applied to developmental as well as acquired disorders If we have speci c brain regions that are already specialized for languageprocessing at birth then it seems reasonable to suppose that a child who is impaired ina modular process must have suffered damage to or maldevelopment of such a systemEnthusiasm for modularity has led to mounting interest from those studying develop-mental disorders with a new discipline of developmental cognitive neuropsychologybeing spawned (Temple 1997) The information processing models derived from thestudy of adults are seen as providing a useful framework for understanding the levelsof representation that need to be investigated and there has been growing awareness of developmental analogues of some acquired disorders such as prosopagnosia (Young ampEllis 1992) subtypes of reading impairment (Castles amp Coltheart 1993) and dyscalculia(Temple 1992)

In my own research however I have experienced mounting dissatisfaction with cog-nitive neuropsychology In large part the dif culties that I outline arise when applyingthis approach to a developing cognitive system However more general problems with thecognitive neuropsychology approach as a whole have also become apparent

My aim in this paper is not to recommend that we abandon cognitive neuropsychologyor that we cease to make contact between developmental and acquired disorders As Ihope to demonstrate I feel that a great deal can be learned by comparing de cits that areseen in children and adults and methodologies and models developed in one context maybe adapted for use in the other My message rather is that we need to contrast as well as

902 BISHOP

TABLE 1Fodorrsquos Characterization of Properties of a Module

domain speci citysystem constrained in terms of the range of information it can access

mandatory processing no voluntary control over whether relevant input is processed

limited central access to intermediate representationsinformation is not available to conscious awareness Eg auditory characteristics of speech sounds orprecise syntactic form of an utterance are dif cult or impossible to report even though the utterancecontaining these was understood

speed complex information processing takes place remarkably quickly

information encapsulationinformation from higher levels is not fed back to lower ones (eg no top down processing occurs)

shallow outputcomputes only a very limited range of representations

xed neural architecturehandled by a circumscribed and dedicated brain region

characteristic breakdown patternsassociated with selective de cits in one area of functioning that cannot be explained in terms of somegeneral loss of capacity

characteristic pace and sequencing in developmentdevelopmental course of a modular function is highlydependent on maturation of endogenous systemsand insensitive to environmental in uences

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compare to recognize what is special about the developmental as opposed to the acquiredcase I hope that readers will nd this critique constructive and that consideration of theissues that arise in a developmental context might feed back and stimulate new thinkingamong those whose primary concern is adult neuropsychology

Speciregc Language Impairment in Children

To illustrate my points I shall draw predominantly on examples from the topic I knowbestmdashspeci c language impairment (SLI) also known as ` developmental dysphasiarsquorsquo or` developmental language disorderrsquorsquo This is de ned as a developmental disorder wherethe childrsquos language acquisition is for no apparent reason out of keeping with otheraspects of development Nonverbal IQ and hearing are within normal limits (see Bishop1994a for an overview) Here we have a disorder that involves by de nition dissociationbetween cognitive domains that are normally associated (language and nonverbal ability)and so it might appear to be an excellent candidate for application of the kinds of modelsand techniques adopted so successfully by cognitive neuropsychologists in the study of acquired aphasia And to be sure SLI in common with other developmental disorders(speci c reading impairment autistic disorder developmental co-ordination disorder)does illustrate that we need more than a single dimension of IQ to account for variationsin childrenrsquos cognitive development The problems arise when we attempt to identify theprimary underlying de cit by looking for fractionations within the language system

There is no shortage of candidate theories (see Bishop 1992 1997 for reviews) Onein uential body of work proposes that the language dif culties are caused by an impair-ment in discriminating rapid or brief auditory stimuli (Tallal amp Katz 1989) According tothis model the breakdown occursat a veryearly point in the information processing chainsomewhere between a representation of an acoustic waveform and it interpretation as amatrix of phonetic features (see Figure 1) Another theory attributes the dif culties tolimitations in phonological short-term memory (Gathercole amp Baddeley 1990) On thisview a phonological representation is generated from spoken input but it decays rapidlyand this affects the childrsquos ability to learn words and grammar A third account maintainsthat specialized mechanisms for grammar acquisition are impaired in SLI (eg Crago ampGopnik 1994) so that the child cannot generate adequate representations at the levels of phrase structure and or cannot map phrase structure onto thematic roles (see Figure 1)My case is that the traditional logic of cognitive neuropsychology is inadequate to dis-criminate these possibilities

LIMITATIONS OF COGNITIVE NEUROPSYCHOLOGY

I Problems for Developmental Applications1 Focus on Dissociations Rather Than Associations

The emphasis that cognitiveneuropsychologyplaces onstudyingdissociations means thatattention is focused on rare cases with unusual patterns of de cit The justi cation is thata single case of dissociation is theoretically more informative than one thousand cases withmultiple impairments because it demonstrates a lack of logical dependence between

DEVELOPMENTAL COGNITIVE NEUROPSYCHOLOGY 903

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de cits The fact that patients with striking patterns of dissociation are the exceptionrather than the rule is irrelevant because the main aim of the enterprise is to build amodel of normal cognition rather than to document the dif culties of neuropsychologicalpatients in general Some have gone so far as to argue that the study of single cases is theonly

valid means of proceeding and that group studies should not be used if onersquos aim isto develop a model of the architecture of the cognitive system (Caramazza 1986)The problem with developmental disorders is that although one may see fractionation

along the lines of major domains of functioning (eg language spatial perception motorco-ordination social cognition numeracy) within any one domain the typical observationis one of a complex pattern of associated impairments rather than the highly selectivede cits that may be found in acquireddisorders And this should not surprise us becausein the developing child an impairment at an early stage of processing would affect all theprocesses downstream of that stage This contrasts with the situation in acquired dis-orders in adults Saffran Marin and Yeni-Komshian (1976) for instance described apatient with ` word deafnessrsquorsquo who was quite unable to do any tasks requiring perceptualanalysis at the phonemic level Although he could not understand spoken languagesemantic and syntactic processes remained intact in his expressive speech Furthermorehe could understand written language In relation to the model shown in Figure 1 writteninput enabled him to generate a representation in the form of a sequence of words whilebypassing the need for auditory and phonological analysis Contrast this with the case of achild who from the earliest stage of language acquisition has a problem in decoding

speech sounds A disruption at this stage of processing would lead to impairment at allsubsequent levels because the systems that would normally be responsible for vocabularylearning and mastery of grammar will not receive adequate input In such a case wewould expect to see a very different pro le of impairment in the child compared to theadult Furthermore we would expect the child to have dif culty in learning to readbecause the necessary substrate of spoken language skills would not be acquired

To take another example we know that in adults a brain lesion can severely impairphonological short-term memory without any obvious effects on comprehension orspeech production (Vallar amp Baddeley 1984) However learning of new vocabulary isimpaired (Baddeley Papagno amp Vallar 1988) In an adult whose vocabulary is alreadyestablished this may be just a minor inconvenience However in a young child who is stilllearning language the consequences would be much more serious In short for the childwho is still developing language a selective impairment at an early stage of processing willhave repercussions throughout all subsequent stages The fact that children are especiallylikely to have associated de cits is not a coincidencemdashit is inevitable given theinterdependence of different stages of processing upon one another in the course of development

Single-case methodology is not helpful for studying associations because we cannotestablish which correlated impairments are just chance associations and which correspondto reliable patterns of co-occurrence To address this issue we need group studies Itcannot be emphasized enough that a focus on group studies does not preclude an interestin individual differences The de cits in children with SLI are not just complex they arealso heterogenous and so a critical question is how to interpret variation in languagepro les Variation from child to child could mean that we are in fact dealing with a group

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of different disorders in which case it is important to nd ways of cleanly distinguishingbetween them However we must remember that some variation may just be meaninglessnoise tests are never perfect indicators of underlying cognitive processes and may besubject to in uences of attention motivation and other random uctuations (see Point 7)

Furthermore some variation in test performance might re ect individual differences incognitive pro le similar to those seen in the normal population after all if we tested anygroup of children on a battery of language measures we would expect to nd differentpro les of strength and weakness from one to the next (cf Goldberg 1995) Clearly thereis no sense in reducing group data to a composite mean when this is not representative of any individual in the group However the answer is not to restrict attention to the study of individual cases but rather to identify reliable clusters of de cit only by studying groupsof individuals can we begin to disentangle what is systematic signal and what is noise fromthe complex patterns of impairment that are seen in a disorder such as SLI

2 Focus on Bottom-up Processing

If we accept that when dealing with a developmental disorder the problem is not somuch one of identifying a dissociation as of trying to account for a cluster of associatedimpairments then it might seem a reasonable strategy to search for the earliest stage of processing at which impairment could be seen For instance suppose a child has weakvocabulary poor understanding of syntax and dif culty in discriminating between speech

sounds If we accept Fodorrsquos proposition that processing of language input is handled byan informationally encapsulated modular system where processing is strictly bottom-up(depicted in Figure 1) then we could conclude that the speech discrimination de citre ects impairment to an earlier stage of processing than the vocabulary or syntacticdif culties and could hence be regarded as the primary de cit that in uences all sub-sequent stages of processing

However this ignores the ample evidence for interaction between levels in languagedevelopment A more realistic model of part of the system is shown in Figure 2 Note thatthis includes top-down as well as bottom-up in uences Consider for instance the pathshown feeding back from syntax to lexicon It is often assumed that children learn wordmeanings simply by recognizing familiar strings of phonemes and deducing the meaningfrom the environmental context However as Gleitman (1994) has cogently arguedalthough this strategy might be useful for learning concrete nouns it is of little help indeducing meanings of other parts of speech such as verbs or abstract nouns Further-more if the visual context were the major cue to learning meaning and structure thencongenitally blind children should have major dif culties in langauge acquisition but onthe whole they do not Landau and Gleitman (1985) considered this issue in an analysisof the language of a blind child who learned to use verbs like ` lookrsquorsquo and ` seersquorsquo appro-priately They proposed that once some grammatical knowledge is available the childmay perform a syntactic analysis on an input sentence containing an unfamiliar word anddeduce its meaning fromthe syntactic frame (syntactic bootstrapping) For instance if anadult describing a cartoon to a blind child says ``Tom really walloped Jerryrsquorsquo the childcan deduce that the word wallop refers to an action in which Tom was agent and Jerry wasobject The grammatical elements associated with a verb provide information as to


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whether it refers to self-caused actions (typically expressed by an intransitive verbmdashiewith a subject and no object such as ` standrsquorsquo or ` swimrsquorsquo) an act that affects anotherrsquosstate (typically a transitive verbwith subject and direct object such as ` kickrsquorsquo or ` ticklersquorsquo)

or a propositional attitude (where the verb typically takes a sentence as a complementsuch as ` thinkrsquorsquo or ` knowrsquorsquo) So if the child has to deduce what ` gorprsquorsquo means a differentconclusion will be reached if the adult says ` John is gorpingrsquorsquo ` John is gorping Maxrsquorsquo or` John gorps that Max is nicersquorsquo It follows that in development syntax and vocabulary arenot independent The child who has poor syntactic skills will have reduced access to thisimportant source of information about word meaning and so vocabulary learning will beretarded

Next consider the path back from lexicon to phonological processing Evidence forthis route comes from studies of phonological short-term memory One might imaginethat the task of repeating nonwords is a pure measure of phonological short-termmemoryuncontaminated by vocabulary knowledge However we now know that the ability toremember novel strings of phonemes is in uenced by their wordlikeness (GathercoleWillis Emslie amp Baddeley 1991) Thus although theoretical interest initially focused onthe question of how phonological STM in uences vocabulary development we nowrecognize that a correlation may re ect in uences in the reverse direction quite simplythe child with a large vocabulary has more opportunity to use knowledge of phonologicalstructure in words to guide performance

These are just two examples of top-down in uences that have been shown to operate inthe course of development Overall Fodorrsquos notion of a modular system that operatesentirely in bottom-up mode might be a reasonable characterization of the stable state thatis achieved in the adult once language is fully learned (although this is debatablemdashseeMarslen-Wilson amp Tyler 1987) however it provides anunrealistic model of processing inthe child who is developing language where there is ample evidence of top-down in u-ences on earlier stages of processing (see Bishop 1997 for further examples) A similar

906 BISHOP

FIG 2 A simpli ed model of early stages of language comprehension indicating top-down as well as bottom-up in uences

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point has been made in the context of developmental dyslexia by Hulme and Snowling(1992) who concluded that ` interaction between systems is probably the norm in devel-opment and it may only be after a very extensive period of development that the relativemodularity or autonomy of different systems in the adult is achievedrsquorsquo They note the

dif culties this leads to in trying to account for developmental reading problems in termsof a highly differentiated modular model derived from adult dataInteraction between levels creates serious dif culties in establishing direction of causa-

tion when multiple de cits are found in children with developmental disorders Considera hypothetical childwho does poorlyon auditory discrimination vocabulary and syntacticcomprehension tests When asked to distinguish between minimal pairs such as bear andpear the child does much more poorly than other children of the same age This istypically interpreted as evidence for an impairment of phonological discrimination How-ever it may be that the child is less familiar with the vocabulary items so that many of thetest items are effectively treated as nonsense words Nonsense words are usually moredif cult to discriminate than are real words Thus the childrsquos weak vocabulary could exerta top-down in uence on performance on the discrimination task And weak vocabularycould itself be a consequence of lack of syntactic knowledge which would prevent thechild fromlearning new word meanings by syntactic bootstrapping In sum it is not validto assume that we can identify primary causes by locating the earliest point in thelanguage comprehension chain at which a de cit can be seen

3 Static Rather Than Developmental Models

In a developmental disorder even if we do nddissociations between de cits these canbe misleadingbecause the pattern of impairment maychange over timeAgoodexample isprovided by a study by Bernstein and Stark (1985) who followed up a group of language-impaired children who were originally tested by Tallal Stark Kallman and Mellits(1981) Tallal and colleagues had demonstrated signi cant de cits in discriminating pairsof tones with brief interstimulus intervals At follow-up several year later many of thesechildren were still impaired on a test of sentence comprehension However when Tallalrsquostest was readministered the original de cit in discriminating tone pairs at short inter-stimulus intervals could no longer be seen children with SLI did as well as controlchildren Thus at follow-up we have a dissociation between intact auditory discriminationand impaired comprehension of sentences Following conventional ` dissociationrsquorsquo logicwe might conclude that the language de cit in these children was not caused by anyauditory dif culty Yet we know from the earlier studies that several years previously thesame children had marked impairments of auditory processing This raises the possibilitythat a slow-maturing auditory perceptual system might leave a lasting legacy of languageimpairment even after ceiling levels of auditory discrimination are reached

Other examples come from studies of individuals who have compensated for develop-mental disordersmdashthat is who have a clear history of reading or language impairmentsbut who do not meet psychometric criteria for developmental dyslexia or SLI when seenin adolescence or adulthood These individuals can often be revealed as having persistingdif culties with tests that require them to process unfamiliar materials (eg nonwordreading or nonword repetition) (Bishop North amp Donlan 1996 Gross-Glenn Jallad


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Novoa Helgren-Lempesis amp Lubs 1990 Stothard Snowling Bishop Chipchase ampKaplan in press) Had we studied these individuals only at one late point in time wemight have concluded that the ability to process nonwords was irrelevant to language andliteracy development However the past history tells a different story and suggests that

the success in everyday language and reading tasks was achieved by adopting atypicalcompensatory strategies For instance a child who has dif culty in segmenting phonemesmay learn to read laboriously by memorizing entire orthographic patterns This strategymay be inef cient but ultimately successful In adulthood we see someone who has majorproblems in nonword reading but adequate real word reading it would be mistakenhowever to use this observation to defend a model of normal reading that assumed norelationship between knowledge of grapheme _ phoneme correspondences and wordrecognition

The more longitudinal studies are carried out in the eld of SLI the more evidencemounts for a changing pro le of language impairments with age highlighting the dangersof basing a model of underlying processes solely on cross-sectional data

Furthermore we have to take into consideration the fact that in the course of devel-opment the nature of representations may change For example in a review of researchWalley (1993) concluded that early phonological development involves a progression fromlarger to more ne-grained units of analysis Initially the child may operate with wholewords or even short phrases simply encoding these in terms of certain salient featuressuch as number of syllables stress and presence of phonetic features such as nasality or

sibilance somewhere in the input (without any speci cation of exactly where) (Waterson1971 1981) Such a child might not be able to distinguish between different syllables thatcontain the same features in different combinations but would nevertheless be able tostore templates of words with incomplete representations of phonetic information AsWalley noted `` Although seldom considered the fact that children produce a certaincontrast does not necessarily imply the presence of that contrast in their perceptualrepresentations for words which might instead be stored and retrieved as unsegmentedwholesrsquorsquo (p 317) By the age of 3 or 4 years most children appear to be aware of thesubsyllabic units of onset and rime but only later probably as a consequence of exposureto print do they recognize the smaller phonemic elements It has been suggested that themain impetus for moving to an analysis at the subsyllabic level is growth in vocabularywhich creates a need to impose a clear organization on lexical storage if words are to berecognized and retrieved rapidly (Jusczyk 1986) Note that this example not only demon-strates the changing nature of representations but also provides another instance of interaction between different levels of representation growth in vocabulary is seen asin uencing the way in which phonological information is encoded

4 Assumption that Modality of Deregcit and Nature of ErrorsRelate to Primary Underlying Cause

In an adult with an acquired disorder we can gain a good picture of the stage of processing that is affected by comparing tasks that involve similar representations indifferent input modalities or by looking at the nature of errors On the surface it seemsvery reasonable to assume that similar logic applies to developmental disorders However

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the case is less clear-cut than it may seem For instance there has been much argumentconcerning the interpretation of impairments in grammatical morphology in childrenwith SLI On the one hand it has been noted that the dif culty experienced by childrenwith SLI in learning the grammatical morphology in a given language is strongly related

to the perceptual salience of in ectional endings so that in English endings such as pasttense ` -edrsquorsquo are often omitted (see Bishop 1997 for a review) However against this viewothers have noted that within a language (and indeed within the same child) the sameword ending such as ` -srsquorsquo may be produced and perceived differentially depending onwhether it functions as a plural a possessive or the nal phoneme in a word such as``horsersquorsquo Also the same grammatical errors of both production and comprehension maybe evident in written as well as spoken language (eg Bishop 1982 Cromer 1978)Authors such as Gopnik and Crago (1991) have regarded such ndings as evidenceagainst auditory de cit accounts of SLI The assumption is that if the problem weresimply that s were dif cult to perceive processing of all forms of s should beimpaired and if auditory discrimination is the basis of the disorder then much betterperformance should be observed with written presentation However this type of assumption is unsafe Low-level general impairments of perceptual or cognitive systemscan lead to unexpected patterns of de cit both because of compensatory mechanisms onthe one hand and because of interactions between different components of a developingsystem on the other If we take the extreme case of children with profound congenitalhearing loss on tests of grammatical comprehension of English they perform very

differently on items that simply require understanding of content words and on thosethat involve appreciating the signi cance of contrasts signalled by morphological end-ings function words and word order regardless of whether or not these are perceptuallysalient (Bishop 1982 1983) Furthermore presentation of sentences in a written formdoes very little to overcome these problems Indeed it was noted that there were somedeaf children who could read aloud every word in a sentence such as the boy is not running or the man is pushed by the elephant but still selected the picture of a boy running and theman pushing the elephant When confronted with complex syntactic constructions deaf children did not just guess at random but rather adopted systematic strategies thatsometimes led to below-chance performance Even those children with facility in a nativesign language had major dif culties in decoding the syntax of Englishmdashpresumablybecause the surface forms used in oral languages to mark grammatical functions (ieword order and bound morphological af xes) are not well suited to processing in thevisual modality where simultaneous rather than sequential grammatical processes are therule Thus hearing loss did not simply lead to a slowing of language acquisition nor did itlead to a predictable pattern of grammatical impairment affecting only non-salient mor-phemes In fact the distinctive response patterns seen in hearing-impaired children wereremarkably similar to those seen in hearing children who had been diagnosed as havingreceptive language disorders The crucial points emphasized by these studies of deaf children are that a general nonlinguistic impairment in auditory perception early indevelopment can (a) have a disproportionately severe impact on the ability to produceand comprehend certain grammatical components of oral language (with different effectson grammatical morphology and vocabulary) and (b) affect written as well as spokenforms of an oral language Note that this pattern of ndings is totally different from


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what one will see if a hearing loss was acquired in adulthood after pro ciency in orallanguage had developed Hearing loss does not just disrupt the input to speci c parts of the language system if acquired early in life it alters the entire course of oral languagedevelopment

It must be stressed that I amnot suggesting that SLI is caused by hearing loss Ratherthe point is that it is dangerous to imagine that we can predict on a priori grounds whatpattern of language impairment would result if the child had a nonspeci c cognitive orperceptual de cit that affected language learningmdashfor example a disorder of auditoryperception such as has been proposed by Tallal (1976) or a limitation of phonologicalshort-term memory as mooted by Gathercole and Baddeley (1990) The impact of ade cit at an early stage of processing can be felt across the whole language system

A further example comes from the domain of reading disability Castles and Coltheart(1993) argued that error patterns could be used to identify which route of a dual-routereading system was impaired in developmental cases just as had been done for acquireddyslexia They produced evidence for developmental forms of two contrasting subtypessurface and phonological dyslexia which together gave a double dissociation Surfacedyslexia is de ned as poor ability to read exception words relative to nonwords whereasphonological dyslexics show the opposite pattern However Snowling and Nation (1997)found in a longitudinal study that not only did many poor readers show characteristics of both surface and phonological dyslexia but that they moved from one subtype to anotherover a two-year period Stanovich Siegel and Gottardo (1997) threw some light on such

paradoxical ndings in a reanalysis of data fromCastles and Coltheart boosted by furtherdata from a younger sample of poor readers They found that the surface dyslexic errorpattern was typical for normally developing children at an early stage of reading abilitymdash that is it could be regarded as a developmental lag rather than indicating impaireddevelopment of one route to reading Furthermore Stanovich and colleagues arguedthat both subtypes of reading disability might lie on a continuum with the precisemanifestation depending on the severity of the underlying phonological impairmentand the amount of exposure to printed words that the child received Thus the errorpattern that one observes may re ect the childrsquos history of reading exposure as well asunderlying cognitive strengths and weaknesses

5 Modules as Hard-wired Innate Systems

Fodorrsquos de nition of a module (Table 1) includes a number of different features thatare logically separable He proposes that if a cognitive process has the characteristics of domain-speci city and information encapsulation then it is likely to be an evolutionaryadaptation with an innate biological basis Those postulating modular explanations of SLIhave emphasised the mounting evidence from both pedigree and twin studies that SLIhas a genetic basis and in some cases may even be caused by a single defective gene(North amp Donlan 1995 Gopnik amp Crago 1991 Hurst Baraitser Auger Graham ampNorrell 1990 Lewis amp Thompson 1992 Tomblin amp Buckwalter 1994) On the basis of such evidence Gopnik and Crago (1991) made the tentative proposal that a single genemight control mechanisms responsible for learning morphological paradigms Howeveraccounts of this work in secondary sources have made more extravagant claims not only

910 BISHOP

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over-exaggerating the selectivity of the morphological de cit (Gazzaniga 1992 cfVargha-Khadem Watkins Alcock Fletcher amp Passingham 1995) but also treating thegenetic etiology of SLI as evidence for an innate grammatical module Thus Jackendoff (1993) argued that

these results strongly suggest that the impairment is genetic and that it speci cally affects theability to construct a mental grammar leaving other cognitive abilities intact In order for thisto be possible there must be at least one gene that is responsible for a special-purpose mentalendowment for language acquisition The part of Universal Grammar having to do withacquiring in ectional endings must not be a general-purpose learning strategy (p 116)

The danger of this logic may be illustrated with a simple analogy between the ability towalk and the ability to talk Like language walking is a ` species universalrsquorsquomdashthat iscommon to all normal humans but not seen in other primatesmdashwhich develops withoutovert instruction in a wide range of environmental circumstances The ability to walkupright across an uneven terrain involves astonishingly complex co-ordination of motorand proprioceptive systems No other primate shares this skill yet all normal humansmaster it without speci c instructionwithin the rst fewyears of life regardless ofwhethertheir local environment is a desert plain a rainforest a snowy mountainside or a Westerncity Attempts to build bipedal robots have met with some success but the end results stillfall far short of a typical 3-year-oldrsquos competence Just as with language though some

unfortunate individuals have a speci c single-gene disordermdashmuscular dystrophymdashwhichselectively interferes with this ability However nobody supposes that because a singlegenetic mutation can cause muscular dystrophy there is a ` gene for walkingrsquorsquo It is appar-ent that walking depends on the integrity of a wide range of underlying systems involvingmuscles nerves and central control processes that regulate balance proprioception andmotor planning Muscular dystrophy hasa speci c effect on just one of these systemsmdashthemusclesmdash but this is suf cient to make walking dif cult or impossible

Those favouring processing accounts of SLI would argue that just the same can be saidfor language The path from gene to behaviour is an immensely complex one and thereare many possible explanations for SLI Genes associated with SLI may operate bydisturbing the development of those brain areas concerned with analysing or retainingtransient auditory stimuli for instance Fodor argued that functions that met the rst fewcriteria for modularity outlined in Table 1 were likely to be ` hard-wiredrsquorsquo and innate sothat they could function rapidly and reliably without requiring a prolonged learningperiod However models of developmental processes suggest a very different storywhereby ` modularityrsquorsquo in the sense of a domain-speci c and informationally encapsul-ated system emerges with experience (see Elman et al 1996 Tucker amp Hirsh-Pasek

1993) The distinction between ` automaticrsquorsquo and ` controlledrsquorsquo processes which mapsclosely onto Fodorrsquos modular central processes distinction seems more a function of practice and experience than of task domain Indeed some highly automatic processsesinvolve arti cial tasks that could not plausibly be regarded as innate such as piano playingor bicycle riding

Nor does localization of a function in a particular brain region imply innateness Thereis plentiful evidence fromacquired dyslexia that the brain regions involved in reading are


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Shallice (1988) notes that inconsistent performance is an indication that underlying repres-entations are intact but not adequately accessed In a similar vein Bishop (1994b) notedthat if a child shows partial mastery of a grammatical structuremdashthat is performance thatis above chance but still defective this poses problems for a representational account of

grammatical de cits because according to such theories a child either does or does notknow a grammatical rule In both acquired and developmental elds there is growingrecognition that one often sees a level of performance that is intermediate betweenunimpaired and random and hence dif cult to explain in terms of defective representa-tions However we must always remember that test performance is only an indirectindicator of underlying cognitive operations and be aware of the possibility that goodperformance as well as errors may misrepresent the individualrsquos capabilities Forinstance Goad and Rebellati (1994) noted that some individuals with SLI did showsome ability to pluralize nonsense words a skill that is typically interpeted as prima facieevidence that the person has knowledge of productive morphological rules However theysuggested that these individuals were explicitly applyingthe taught rule ` add -s to formapluralrsquorsquo Not only did this lead to slow and effortful production but detailed phoneticanalysis showed that the apparently correct plural ` -srsquorsquo forms produced by language-impaired individuals lacked voicing assimilation for instance when asked for the plural of ` wugrsquorsquo the response was WL gS rather than WL gZ The point stressed by theseresearchers is that correct performance on a language test need not necessarily re ecttrue competence in underlying ability Grammatical morphemes might be used without

appreciation of their syntactic signi cance being applied consciously after explicitinstruction in their useA second crucial feature of processing theories is that they predict that the ability to do

linguistic tasks will vary depending on task demands In the study of semantic de cits inaphasia it has been demonstrated that some patients do much better in tests of compre-hension or naming if a long interval (eg 30 seconds) elapses between each response andthe next trial than if a standard presentation rate (eg 1 to 2 seconds between items) isused (Forde amp Humphreys 1995 McNeil Cipolotti amp Warrington 1994 Warrington ampMcCarthy 1983) Rather less has been done on the effect of presentation rate on gram-matical processing although comprehension of complex sentences has been shown to beimpaired in normal adults at rapid presentation rates (Miyake Carpenter amp Just 1994)In a study of children with SLI McCroskey and Thompson (1973) showed that foryounger children performance on a sentence comprehension task improved signi cantlywhen the sentences were presented at a rate of 29 syllables per second compared with 50syllables per second indicating that the children had the necessary linguistic knowledgeto do the task but were poor at deploying it under real time constraints

One factor that has been explored in the developmental context is the notion of trade-

offs between different levels of processing Because cognitive neuropsychology adopts amodular framework the possibility of interactions between different levels of processingis seldom considered but from a developmental perspective one would expect themTrade-offs make sense if we assume that there is a limited-capacity system that handlesseveral linguistic operations simultaneously so that complexity at one level can lead toerrors at another For instance if we restrict ourselves to vocabulary that the child knowsbut include some words that are relatively infrequent and others that are common can we


8122019 Bishop 1997


in uence the dif culty of a grammatical comprehension test by in uencing the ease of lexical access Does phonological complexity or word length affect the ability to under-stand a complex sentence If we nd interactions between language levels this would besupportive of a processing explanation of comprehension dif culties To my knowledge

experimental studies of this kind have not been conducted on comprehension in childrenwith SLI but evidence for trade-offs has been found in analyses of childrenrsquos languageoutput (Crystal 1987 Masterson amp Kamhi 1992 Panagos amp Prelock 1982)

Notions of limited processing capacity make testable predictions that ability to produceand comprehend language will depend not just on the nature and complexity of therepresentations that are accessed but also on the overall processing demands placed onthe individual In contrast to the modular approach derived from cognitive neuropsy-chology they steer us away from looking at different components of language in isolationand draw attention to the trade-offs that may exist between different levels of processingand to the effects of variables such as speech rate on linguistic processing Processingaccounts predict that we may be able to manipulate level of performance with particularsentence structures by changing the processing demands of a task If so this would notonly further our theoretical understanding of SLI but would also have implications forintervention

7 Problems in Interpreting Differential Deregcit

The textbook case of a patient who is entirely normal on tasks measuring one set of cognitive operations (X) and completely unable to do another set (Y) is very rarelyobserved even if one restricts consideration to acquired cases with focal lesions Moreoften arguments in cognitive neuropsychology are based on evidence of differential de citmdashthat is the patient might be impaired in both X and Y but the impairment inX is more severe However as Wilding (1989) pointed out researchers seldom makeexplicit their criteria for deciding that a difference between X and Y should be regardedas a signi cant dissociation When one attempts to specify such criteria one comes upagainst methodological dif culties related to psychometric characteristics of tests espe-cially item dif culty and item reliability Most researchers are aware of interpretativeproblems created by oor and ceiling effects For instance in Figure 3 the control andSLI groups differ signi cantly on Test X but not on Test Y but we would be wary of assuming that there was differential de cit in X because performance on Y is near ceilingfor both groups and hence by choosing too easy a test we may have masked a realdifference between groups What is much less well appreciated is that even when groupperformance is off oor or ceiling differences in the relative dif culty of items in twotests can lead to spurious ` dissociationsrsquorsquo Chapman and Chapman (1973) recommendedthat researchers attempt to match the dif culty level of tasks that are to be compared anduse items that give good discrimination within a control group wherever possible Theyalso illustrated the extent to which test reliability can in uence the size of differences inscores between two groups Figure 4 shows real data from a multiple-choice analogies testobtained by these authors from 49 people with schizophrenia and 206 normal controlsFrom within the same test they selected items to form a high-reliability (X) and a low-reliability (Y) version Only the more reliable version showed a signi cant de cit in the

914 BISHOP

8122019 Bishop 1997


group with schizophrenia The point emphasized by Chapman and Chapman is that thetwo tests were selected to be equivalent both in terms of item content and in terms of overall dif culty in the control group It is clearly the difference in test reliability that isreponsible for the differential de cit of the schizophrenic group Yet if X and Y haddifferent types of content we might easily have been misled into assuming that the peoplewith schizophrenia had a selective de cit in carrying out the cognitive operations involved

in Test X In general the demonstration of differential de cit is less of a problem if ourcontrol task (Y) is a well-standardized psychometric instrument because it is then reason-able to suppose that Y is at least as discriminating and reliable as an experimental test (X)and so if we nd that people who are matched on Yperform differentlyonX it is unlikelythat this is because Y is less sensitive However where both X and Y are assessed byexperimental tasks Chapman and Chapman recommended that researchers match the


FIG 3 Differential de cit complicated by a ceiling effect ( ctitious data)

FIG 4 Effect of test reliability on sensitivity to de cit Data from Chapman and Chapman(1973) Reliability isassessed in terms of coef cient alpha a measure of how well individual items correlate with the test total (ieinternal consistency)

8122019 Bishop 1997


tasks on discriminating power and reliability in order to have con dence in interpretingdissociations

In classic cognitive neuropsychology these kinds of dif culty are implicitly recognizedby those who stress the particular importance of double dissociations for informing theory

(Milner amp Teuber 1968) In short if we have two patients who showtheopposite

patternsof de cit with one selectively impaired on X and the other selectively impaired on Y thenit would seemthat we are in a stronger position to conclude that X and Yare independentfaculties and to reject any simple explanation in terms of ` generalrsquorsquo task factors such astest reliability or dif culty Even here however some awareness of psychometric prin-ciples is needed Bates Appelbaum and Allard (1991) noted that some dissociationsbetween measures can be expected by chance alone (this being particularly likely whentest reliability is low and when reliance is placed on data from a single case)

BEYOND COGNITIVE NEUROPSYCHOLOGY

Studying Interaction and Change in LanguageImpairments

Given the dif culties encountered when trying to apply the traditional methods of cog-nitive neuropsychology to a developmental disorder what are the alternative approaches

one can adopt The traditional kind of study where children with SLI are compared witha control group on one or more language tests is usually a useful rst step in trying toelucidate the nature of SLI but it is unlikely to resolve questions about primacy of speci c cognitive de cits Striking dissociations are rare in children and even whenthey occur their interpretation is often ambiguous because of changing patterns of impairment with age Associations between de cits are even more dif cult to interpretbecause they could re ect bottom-up in uences on high-level processes top-down in u-ences on low-level processes or it could be that the de cits are causally unconnected buttend to co-occur because they are mediated by adjacent brain areas This does not meanthat we should abandon attempts at furthering our understanding of psycholinguisticprocesses in SLI only that we need to recognize that converging evidence from differentmethodologies will be needed To conclude this paper a brief overview of differentmethods is offered for consideration

Language Age-Matched Controls

One of the commonest strategies used in the study of SLI is to compare a language-

impaired group with a younger control group matched on some index of ` language agersquorsquoThe rationale for this approach is that it should give us some indication of whether aspeci c impairment on a test X is disproportionate to the childrsquos language level If not itcould be argued that poor performance on X is simply a consequence of low languageskills rather than being of primary importance in causing the language dif culties How-ever if children with SLI do even more poorly than language-matched controls thisindicates that we canrsquot just dismiss the de cit as secondary

916 BISHOP

8122019 Bishop 1997


There are several dif culties inherent in this approach First it is an exceedinglyconservative method A lack of difference between groups does not tell us much exceptthat the impairment could be a secondary one As the children with SLI are older than thecontrol group they are likely to be more advanced in general cognitive development and

to have better attention and a better ability to develop strategies for doing an experimentaltask and these could counteract any effect of underlying impairment Second ` age-equivalentrsquorsquo scores can vary substantially from one test to another and it can be dif cultto know which language test children should be matched on (see Bishop 1997) Thirdthe psychometric issues involved in looking for differential de cit (see earlier) are criticalin this kind of design but are often ignored

Comparison with Other Groups with Known Level of

ImpairmentWhen considering the impact of relatively peripheral impairments on languagedevelop-

mentmdashthat is those affecting sensory or motor processes useful insights can be obtainedby studying children suffering from conditions known to affect these Bishoprsquos (19821983) studies of comprehension of English grammar in children with hearing impairmentprovide one example Contrary to expectation these studies revealed a distinctive patternof grammatical dif culties cutting across input modality in such children and thusoffered indirect supporting evidence to those who would argue that an early auditory

impairment can distort acquisition of oral syntax Another example comes from studies of children who are dysarthric or anarthric and therefore nd oral speech dif cult orimpossible because of impairments of motor control These children allowone to addressquestions such as how far articulatory coding plays a role in memory or phonologicalsegmentation (eg Bishopamp Robson 1989a 1989b) and whether experience of producinglanguage is critical for the development of understanding (Bishop Byers-Brown ampRobson 1990) In general these studies have revealed surprisingly intact abilities indomains of phonological and syntactic processing in children who cannot produce clearspeech and they therefore make us less ready to assume that comprehension dif cultiesin children with SLI are due to their expressive limitations

Experimental Studies on ``Trade-offsrsquorsquo and CapacityLimitations

A growing interest in processing accounts of language development and disordersencourages us to do more studies using a within-subjects design where the goal is tosee how various experimental manipulations affect the childrsquos ability to understand asopposed to the more traditional between-subjects studies where two or more groups arecompared Methods include investigating the effects of varying such factors as rate of presentation background noise prosody and so on on childrenrsquos understanding as wellas within the same task varying dif culty at different levels of processing such asphonology semantics and syntax A nice feature of such studies is the potential theyhave for providing results that are useful in intervention by specifying which parametersmake it easier or more dif cult for children to process language


8122019 Bishop 1997


Longitudinal Studies

The potential importance of longitudinal studies for addressing causal questions hasalready been emphasized Such methods have not been widely used in the study of SLI and application of sophisticated statistical modelling (see for instance MagnussonBergman Rudinger amp To umlrestad 1989 for examples) has barely been attempted Never-theless even with a fairly simple methodological approach longitudinal studies can beinvaluable in helping clarify the direction of causal relationships in normal development(eg Gathercole Willis Emslie amp Baddeley 1992) for highlighting the role that earlyimpairments may play in causing later de cits (eg Bernstein amp Stark 1985) and forthrowinglight onquestionsof classi cation(seeeg Bishop 1994c BishopampEdmundson1987)

Modelling the Learning Process and Simulating Effects ofImpairment at a Given Stage

Newdevelopments in dynamic systems theory (Thelen ampSmith 1993) and connectionistmodelling (Elman et al 1996) are making it possible to develop simulations of develop-mental change in contrast to previous computational approaches which were based onstatic information-processing systems These have the potential to let us see how thenature of representations changes as an organism interacts with its environment and how

uctuations either in the biological substrate or in the input it receives may affect devel-oping language processes

Intervention Studies

The ultimate test of a hypothesis is through experimental manipulation If one believesthat one has identi ed the primary process that is implicated in SLI then by amelioratingthat de cit one should be able to show bene cial effects on other aspects of languagedevelopment For instance Tallal et al (1996) exposed language-impaired children toacoustically modifed speech in which the duration of the speech signal was prolonged andthe transitional elements were ampli ed Control children received a similar package of interventions but using unmodi ed speech and computer games based on discrimina-tions that did not involve rapid processing The outcomes reported by Tallal and collea-gues were dramatic with children who received the ` temporal processingrsquorsquo interventionshowing signi cantly greater improvement than control children on language measuresThis work which has excited considerable controversy is still at an early phase andfurther evaluation studies are under way It remains unclear which components of theintervention package are critical If the early promise of the method is ful lled withauditory training producing improved language abilities in everyday contexts this wouldbe the strongest support yet for the view that linguistic dif culties in these children aresecondary to more fundamental auditory limitations

Another example comes from a study brie y described by Gillam and van Kleek(1996) They found that training language-impaired children in phonological awareness

918 BISHOP

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led to improvements in their nonwordrepetition without in uencing real word repetitionThis supports the viewthat poor nonword repetition in children with SLI may have moreto do with how phonological information is initially encoded in memory than with limitedstorage capacity or rapid decay of stored information (see Bishop 1997)

Although applications to intervention are frequently cited by researchers as the justi-cation for doing experimental studies all too often the link with clinical practice is nevermade It is time for researchers to recognize that intervention studies are not just anoptional applied adjunct to experimental work but that they provide the best methodavailable for evaluating hypotheses and unconfounding correlated factors

Conclusion

It must be stressed that I am not saying that cognitive neuropsychology has nothing tooffer developmental psychology Case studies of adults with acquired lesions can provideimportant insights into the stages of processing that are involved in a particular cognitiveprocess and they can lead to the development of ingenious tasks for pinpointing theunderlying cause of impaired language performance However it is dangerous to assumethat a model of cognitive processing that is derived from the study of adults can beapplied without modi cation to children there is ample evidence that the nature of underlying representations may evolve in the course of development and there may be

far more interaction between levels of processing in children than adults When inter-preting dissociations one needs to be aware that the pro le of impairment can changewith age and that an impairment affecting one stage of processing may have bottom-up ortop-down in uences on the development of other stages If the same child who isclassi ed as a ` surface dyslexicrsquorsquo at one point in time turns into a ` phonologicaldyslexicrsquorsquo later in development then this questions the rationale of treating these ascomplementary disorders involving impairment to different pathways Furthermore testsensitivity and reliability will in uence how easy it is to show differential de cit if we

nd a child who is impaired in Test X but not in Test Y we tend to assume that this isbecause X is an index of some underlying cognitive process (A) that is compromisedwhereas the function B measured by Test Y is still intact However as argued aboveit could be that X is just a more sensitive reliable and or valid index of A than Test Yas an index of B The fact that different cognitive functions may show different growthtrends in the normal population complicates the picture yet further Test X may be anexcellent index of A in 6-year-olds but be insensitive for 12-year-olds Finally it isimportant to distinguish whether our primary goal is to use disorders to understandnormal development or to develop a model of the disorder itself If our aim is toincrease our understanding of SLI we need to focus not so much on demonstratingdissociations as on interpreting complex patterns of impairment In this context thesingle case approach is singularly inappropriate because we cannot tell whether the co-occurrence of impairments is a chance occurrence or a systematic pattern We need tostudy groups of individuals in order to look at correlations between impairments indifferent processes


8122019 Bishop 1997


REFERENCES

Albert ML amp Bear D (1974) Time to understand A case study of word deafness with reference tothe role of time in auditory comprehension Brain 97 373 _ 384

Baddeley A Papagno C ampVallar G (1988) When long-termlearning depends on short-termstorage Journal of Memory and Language 27 586 _ 595

Bates E Appelbaum M amp Allard L (1991) Statistical constraints on the use of single cases inneuropsychological research Brain and Language 40 295 _ 329

Berndt RS Basili A amp Caramazza A (1987) Dissociation of functions in a case of transcorticalsensory aphasia Cognitive Neuropsychology 4 79 _ 107

Bernstein LE amp Stark RE (1985) Speech perception development in language-impaired children A4-year follow-up study Journal of Speech and Hearing Research 50 21 _ 30

Bishop DVM (1982) Comprehension of spoken written and signed sentences in childhood languagedisorders Journal of Child Psychology and Psychiatry 23 1 _ 20

Bishop DVM (1983) Comprehension of English syntax by profoundly deaf children Journal of Child Psychology and Psychiatry 24 415 _ 434

Bishop DVM (1992) The underlying nature of speci c language impairment Journal of Child Psy-chology and Psychiatry 33 1 _ 64

Bishop DVM (1994a) Developmental disorders of speech and language In M Rutter L Hersov amp ETaylor (Eds) Child and adolescent psychiatry (pp 546 _ 568) Oxford Blackwell Scienti c

Bishop DVM (1994b) Grammatical errors in speci c language impairment Competence or perfor-mance limitation Applied Psycholinguistics 15 507 _ 549

Bishop DVM (1994c) Is speci c language impairment a valid diagnostic category Genetic andpsycholinguistic evidence Philosophical Transactions of the Royal Society Series B 346 105 _ 111

Bishop DVM (1997) Uncommon understanding Development and disorders of language comprehension inchildren Hove Psychology Press

Bishop DVM Byers-Brown B amp Robson J (1990) The relationship between phoneme discrimina-tion speech production and languagecomprehensionin cerebral-palsied individuals Journal of Speechand Hearing Research 33 210 _ 219

Bishop DVM amp Edmundson A (1987) Language-impaired four-year-olds Distinguishing transientfrom persistent impairment Journal of Speech and Hearing Disorders 52 156 _ 173

Bishop DVM North T amp Donlan C (1995) Genetic basis of speci c language impairment Evidencefrom a twin study Developmental Medicine and Child Neurology 37 56 _ 71

Bishop DVM North T amp Donlan C (1996) Nonword repetition as a behavioural marker forinherited language impairment Evidence from a twin study Journal of Child Psychology and Psychia-try 37 391 _ 403

Bishop DVM amp Robson J (1989a) Unimpaired short-term memory and rhyme judgement in con-genitally speechless individuals Implications for the notion of ` articulatory codingrsquorsquo Quarterly Journal of Experimental Psychology 41A 123 _ 140

Bishop DVM amp Robson J (1989b) Accurate nonword spelling despite congenital inability to speakPhoneme _ grapheme conversion does not require subvocal articulation British Journal of Psychology 80 1 _ 13

Caramazza A (1986) On drawing inferences about the structure of normal cognitive systems fromtheanalysis of patterns of impaired performance The case for single-patient studies Brain andCognition 5 41 _ 66

Castles A amp Coltheart M (1993) Varieties of developmental dyslexia Cognition 47 149 _ 180Chapman LJ amp Chapman JP (1973) Problems in the measurement of cognitive de cit Psychological

Bulletin 79 380 _ 385Chapman RS (1992) Processes in language acquisition and disorders St Louis MO Mosby Year BookClahsen H (1989) The grammatical characterization of developmental dysphasia Linguistics 27 897 _

920Coltheart M (1987) Functional architecture of the language processing system In M Coltheart G

Sartori amp R Job (Eds) The cognitive neuropsychology of language (pp 1 _ 25) London LawrenceErlbaum Associates Ltd

920 BISHOP

8122019 Bishop 1997


Crago MB amp Gopnik M (1994) From families to phenotypes Theoretical and clinical implicationsof research into the genetic basis of speci c language impairment In R Watkins amp M Rice (Eds)Speci c language impairments in children (pp 35 _ 51) Baltimore MD Paul H Brookes

Cromer RF (1978) The basis of childhood dysphasia A linguistic approach In M A Wyke (Ed)Development dysphasia (pp 85 _ 134) London Academic Press

Crystal D (1987) Towards a ` bucketrsquorsquo theory of language disability taking account of interactionbetween linguistic levels Clinical Linguistics and Phonetics 1 7 _ 22Elman J Bates E Johnson MH Karmiloff-Smith A Parisi D amp Plunkett K (1996) Rethinking

innateness A connectionist perspective on development Cambridge MA MIT PressFodor JA (1983) The modularity of mind Cambridge MA Bradford BooksForde E amp Humphreys GW (1995) Refractory semantics Memory 3 265 _ 307Gardner H amp Zurif E (1975) BEE but not BE Oral reading of single words in aphasia and alexia

Neuropsychologia 13 181 _ 190Gathercole SE amp Baddeley AD (1990) Phonological memory de cits in language disordered chil-

dren Is there a causal connection Journal of Memory and Language 29 336 _ 360Gathercole SE Willis C Emslie H amp Baddeley AD (1991) The in uences of syllables and

wordlikeness on childrenrsquos repetition of nonwords Applied Psycholinguistics 12 349 _ 367Gathercole SE Willis C Emslie H amp Baddeley AD (1992) Phonological memory and vocabulary

development during the early school years Alongitudinal study Developmental Psychology 28 887 _ 898Gazzaniga MS (1992) Naturersquos mind London Penguin BooksGillam RB ampVan Kleek A (1996) Phonological awareness training and short-termworking memory

Clinical implications Topics in Language Disorders 17 72 _ 81Gleitman LR (1994) Words words words Philosophical Transactions of the Royal Society Series B 346

71 _ 77Goad H amp Rebellati C (1994) Pluralization in familiar language impairment In J Matthews (Ed)

Linguistic aspects of familial language impairment Special issue of theMcGill working papers in linguistics Vol 10 (pp 24 _ 40)

Goldberg E (1995) Rise and fall of modular orthodoxy Journal of Clinical and Experimental Neurop-sychology 17 193 _ 208

Gopnik M amp Crago M (1991) Familial aggregation of a developmental language disorder Cognition 39 1 _ 50

Gross-Glenn K Jallad B Novoa L Helgren-Lempesis V amp Lubs HA (1990) Nonsense passagereading as a diagnostic aid in the study of adult familial dyslexia Reading and Writing 2 161 _ 173

Haarman HJ amp Kolk HHJ (1991) A computer model of the temporal course of agrammaticsentence understanding The effects of variation in severity and sentence complexity CognitiveScience 15 49 _ 87

Hulme C amp Snowling M (1992) De cits in output phonology An explanation of reading failureCognitive Neuropsychology 9 47 _ 72

Hurst JA Baraitser M Auger E Graham F amp Norell S (1990) An extended family with adominantly inherited speech disorder Developmental Medicine and Child Neurology 32 352 _ 355

Jackendoff R (1993) Patterns in the mind Hemel Hempstead Harvester WheatsheafJohnston J (1994) Cognitive abilities of children with language impairment In R Watkins amp M Rice

(Eds) Speci c language impairments in children (pp 107 _ 121) Baltimore Paul H BrookesJusczyk P (1986) Toward a model of the development of speech perception In JS Perkell amp DH

Klatt (Eds) Invariance and variability in speech processes (pp 1 _ 19) Hillsdale NJ Lawrence ErlbaumAssociates Ltd

Lan dau B amp Gleitman L (1985) Language and experience Evidence from the blind child CambridgeMA Harvard University Press

Lewis BA amp Thompson LA (1992) A study of developmental speech and language disorders intwins Journal of Speech and Hearing Research 35 1086 _ 1094

Magnusson D Bergman LR Rudinger G amp To umlrestad B (1989) Problems and methods in longitudinal research Stability and change Cambridge Cambridge University Press

Marslen-Wilson W amp Tyler L (1987) Against modularity In JL Gar eld (Ed) Modularity in


8122019 Bishop 1997


knowledge representation and natural-language understanding (pp 37 _ 62) Cambridge MA MITPress

Masterson JJ amp Kamhi AG (1992) Linguistic trade-offs in school-age children with and withoutlanguage disorders Journal of Speech and Hearing Research 35 1064 _ 1075

McCroskey RL amp Thompson NW (1973) Comprehension of rate controlled speech by children

with speci c learning disabilities Journal of Learning Disabilities

6

621 _

628McNeil JE Cipolotti L amp Warrington EK (1994) The accessibility of proper names Neuropsy-chologia 32 193 _ 208

Milner B ampTeuber H-L (1968) Alterations of perception and memory in man Re ections on methodin L Weiskrantz (Ed) Analysis of behavioral change (pp 268 _ 375) New York Harper and Row

Miyake A Carpenter PA amp Just MA (1994) A capacity approach to syntactic comprehensiondisorders Making normal subjects perform more like aphasic patients Cognitive Neuropsychology 11 671 _ 717

Panagos JM amp Prelock PA (1982) Phonological constraints on the sentence productions of lan-guage-disordered children Journal of Speech and Hearing Research 25 171 _ 177

Saffran EM Marin OSM ampYeni-Komshian GH (1976) An analysisof speech perception in worddeafness Brain and Language 3 209 _ 228

Schwartz M Saffran EM amp Marin OSM (1980) The word order problem in agrammatism IComprehension Brain and Language 10 249 _ 262

Shallice T (1988) From neuropsychology to mental structure Cambridge Cambridge University PressSnowling M amp Nation K (1997) Language phonology and learning to read In C Hulme amp M

Snowling (Eds) Dyslexia Biology cognition and intervention London Whurr PublishersStanovich KE Siegel LS amp Gottardo A (1997) Progress in the search for dyslexia sub-types In C

Hulme amp M Snowling (Eds) Dyslexia Biology cognition andintervention London Whurr PublishersStothard SE Snowling MJ Bishop DVM Chipchase BB amp Kaplan CA (in press) Language-

impaired preschoolers A follow-up into adolescence Journal of Speech Language and Hearing Research

Tallal P (1976) Rapid auditory processing in normal and disordered language development Journal of Speech and Hearing Research 19 561 _ 571

Tallal P amp Katz W (1989) Neuropsychological and neuroanatomical studies of developmental lan-guage reading disorders Recent advances In C von Euler I Lundberg amp G Lennerstrand (Eds)Brain and reading (pp 183 _ 196) New York Stockton Press

Tallal P Miller SL Bedi G Byma G Wang X Najarajan SS Schreiner C Jenkins WM ampMerzenich MM (1996) Language comprehension in language-learning impaired children im-proved with acoustically modi ed speech Science 271 81 _ 84

Tallal P Miller S amp Fitch RH (1993) Neurobiological basis of speech A case for the pre-eminenceof temporal processing In P Tallal AM Galaburda RR Llinas amp C von Euler (Eds) Temporal information processing in the nervous system ( Annals of the New York Academy of Sciences Vol 682 pp27 _ 47) New York New York Academy of Sciences

Tallal P Stark R Kallman C amp Mellits D (1981) A re-examination of some nonverbal perceptualabilities of language-impaired and normal children as a function of age and sensory modality Journal of Speech and Hearing Research 24 351 _ 357

Temple CM (1992) Developmental dyscalculia In SJ Segalowitz amp I Rapin (Eds) Handbook of neuropsychology Vol 7 Section 10 Child neuropsychology Part 2 (pp 211 _ 222) Amsterdam ElsevierScience

Temple CM (1997) Developmental cognitive neuropsychology Journal of Child Psychology and Psy-chiatry 38 27 _ 52

Thele n E amp Smith LB (1993) A dynamic systems approach to the development of cognition andaction Cambridge MA MIT Press

Tomblin JB amp Buckwalter PR (1994) Studies of genetics of speci c language impairment In RWatkins amp M Rice (Eds) Speci c language impairments in children (pp 17 _ 34) Baltimore MD PaulH Brookes

Tucker M amp Hirsh-Pasek K (1993) Systems and language Implications for acquisition In LB

922 BISHOP

8122019 Bishop 1997


Smith amp E Thelen (Eds) A dynamic systems approach to development Applications (pp 359-384)Cambridge MA MIT Press

Vallar G amp Baddeley AD (1984) Phonological short-term store phonological processing and sen-tence comprehension A neuropsychological case study Cognitive Neuropsychology 1 121 _ 141

Van der Lely HKJ (1994) Canonical linking rules Forward versus reverse linking in normally

developing and speci cally language-impaired children Cognition

51

29 _

72Vargha-Khadem F Watkins K Alcock K Fletcher P amp Passingham R (1995) Praxic and non-verbal cognitive de cits in a large family with a genetically transmitted speech and language disorderProceedings of the National Academy of Sciences 92 930 _ 933

Walley AC (1993) The role of vocabulary development in childrenrsquos spoken word recognition andsegmentation ability Developmental Review 13 286 _ 350

Warrington EK amp McCarthy R (1983) Category speci c access dysphasia Brain 106 859 _ 878Warrington EK amp McCarthy RA (1987) Categories of knowledge Further fractionations and an

attempted integration Brain 110 1273 _ 1296Warrington EK amp Shallice T (1979) Semantic access dyslexia Brain 102 43 _ 63Waterson N (1971) Child phonology A prosodic view Journal of Linguistics 7 179 _ 211Waterson N (1981) A tentative developmental model of phonological representation In T Myers J

Laver amp J Anderson (Eds) The cognitive representation of speech (pp 323 _ 333) Amsterdam NorthHolland Publishing Co

Wilding J (1989) Developmental dyslexics do not t in boxes Evidence from the case studiesEuropean Journal of Cognitive Psychology 1 105 _ 127

Young AW amp Ellis HD (1992) Visual perception In SJ Segalowitz amp I Rapin (Eds) Handbook of neuropsychology Vol 7 Section 10 Child neuropsychology Part 2 (pp 1 _ 14) Amsterdam ElsevierScience

Original manuscript received 16 January 1997 Accepted revision received 19 May 1997


8122019 Bishop 1997


analysing patterns of de cit in brain-damaged individuals (see Coltheart (1987) andShallice (1988) for reviews) The emphasis was largely on case studies that demonstratedhighly selective patterns of cognitive de cit and could inform theory by demonstratingthe relative independence of different cognitive processes A great deal of evidence has

accumulated to support the view that not only is language processing largely independentof other cognitive functions but within the language systemthere are independent stagesthat may be selectively disrupted For instance one may see patients who lose the abilityto understand spoken language while retaining the ability to repeat (eg Berndt Basili ampCaramazza 1987) or who are able to read content words but not function words (Gardneramp Zurif 1975) others may have particular dif culty in understanding sentences wherewordorder is critical (Schwartz Saffran amp Marin 1980) in yet other cases there may beloss of the ability to name or comprehend items of a given semantic class (eg Warringtonamp McCarthy 1987) Evidence such as this has been used to develop information proces-sing models of language comprehension as involving a sequence of repesentational stageseach largely independent of the other (eg Figure 1)

The publication of Fodorrsquos (1983) in uential book The Modularity of Mind incorpor-ated many of the ideas that had developed in cognitive neuropsychology by proposingthat much of our cognitive processing is modular According to Fodor a module is adomain-speci c and informationally encapsulated brain systemresponsible for handling aparticular type of mental representation which has the properties listed in Table 1 Thismay be illustrated by considering how the brain handles speech perception Domain

speci city refers to the fact that the mechanisms involved in speech perception appearto be distinct from those used for other kinds of auditory analysis and operate only onacoustic signals that are taken to be utterances Information encapsulation refers to thefact that modular processing cannot be in uenced by higher cognitive operations Thisresults in mandatory processing one cannot easily ignore incoming speechmdasheven if attention is switched away from interpreting utterances one will immediately respondon hearing a salient signal such as onersquos own name Processing in a modular systemis fastand automatic in contrast to central processes concerned with long-term memory andreasoning which are typically slow optional and general-purpose able to combine infor-mation froma variety of sources In Fodorrsquos scheme processing of language is modular upto the stage where a propositional representation is generated Later stages of under-standingmdashthat is incorporating general and social knowledge to interpret the utterancemdash are seen as involving central processes and do not have the characteristics of modules

Fodor used evolutionary arguments to support the idea that a complex processor thatrapidly performs a dedicated function (ie a module) is likely to be innately pre-pro-grammed and the nding that damage to a particular brain region can lead to a selectiveimpairment in a particular stage of language processing has been taken as evidence forthis

900 BISHOP

FIG 1 Information processing model showing the sequence of representations generated in comprehendingthe sentence ` the sh is on the tablersquorsquo Pragmatic in uences on interpretation (handled by Fodorrsquos so-called` central processesrsquo rsquo) are not shown and processing is depicted as entirely bottom-up

8122019 Bishop 1997


901

8122019 Bishop 1997





902 BISHOP











8122019 Bishop 1997










8122019 Bishop 1997








904 BISHOP

8122019 Bishop 1997









8122019 Bishop 1997






906 BISHOP


8122019 Bishop 1997









8122019 Bishop 1997









908 BISHOP

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8122019 Bishop 1997








910 BISHOP

8122019 Bishop 1997










8122019 Bishop 1997


8122019 Bishop 1997









8122019 Bishop 1997







914 BISHOP

8122019 Bishop 1997







8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


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920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

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922 BISHOP

8122019 Bishop 1997






51

29 _










8122019 Bishop 1997


901

8122019 Bishop 1997





902 BISHOP











8122019 Bishop 1997










8122019 Bishop 1997








904 BISHOP

8122019 Bishop 1997









8122019 Bishop 1997






906 BISHOP


8122019 Bishop 1997









8122019 Bishop 1997









908 BISHOP

8122019 Bishop 1997






8122019 Bishop 1997








910 BISHOP

8122019 Bishop 1997










8122019 Bishop 1997


8122019 Bishop 1997









8122019 Bishop 1997







914 BISHOP

8122019 Bishop 1997







8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


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920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

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8122019 Bishop 1997





902 BISHOP











8122019 Bishop 1997










8122019 Bishop 1997








904 BISHOP

8122019 Bishop 1997









8122019 Bishop 1997






906 BISHOP


8122019 Bishop 1997









8122019 Bishop 1997









908 BISHOP

8122019 Bishop 1997






8122019 Bishop 1997








910 BISHOP

8122019 Bishop 1997










8122019 Bishop 1997


8122019 Bishop 1997









8122019 Bishop 1997







914 BISHOP

8122019 Bishop 1997







8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


REFERENCES
























920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

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8122019 Bishop 1997










8122019 Bishop 1997








904 BISHOP

8122019 Bishop 1997









8122019 Bishop 1997






906 BISHOP


8122019 Bishop 1997









8122019 Bishop 1997









908 BISHOP

8122019 Bishop 1997






8122019 Bishop 1997








910 BISHOP

8122019 Bishop 1997










8122019 Bishop 1997


8122019 Bishop 1997









8122019 Bishop 1997







914 BISHOP

8122019 Bishop 1997







8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


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920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

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8122019 Bishop 1997








904 BISHOP

8122019 Bishop 1997









8122019 Bishop 1997






906 BISHOP


8122019 Bishop 1997









8122019 Bishop 1997









908 BISHOP

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8122019 Bishop 1997








910 BISHOP

8122019 Bishop 1997










8122019 Bishop 1997


8122019 Bishop 1997









8122019 Bishop 1997







914 BISHOP

8122019 Bishop 1997







8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


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920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

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8122019 Bishop 1997









8122019 Bishop 1997






906 BISHOP


8122019 Bishop 1997









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908 BISHOP

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8122019 Bishop 1997








910 BISHOP

8122019 Bishop 1997










8122019 Bishop 1997


8122019 Bishop 1997









8122019 Bishop 1997







914 BISHOP

8122019 Bishop 1997







8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


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920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

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8122019 Bishop 1997






906 BISHOP


8122019 Bishop 1997









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908 BISHOP

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8122019 Bishop 1997








910 BISHOP

8122019 Bishop 1997










8122019 Bishop 1997


8122019 Bishop 1997









8122019 Bishop 1997







914 BISHOP

8122019 Bishop 1997







8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


REFERENCES
























920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

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8122019 Bishop 1997









8122019 Bishop 1997









908 BISHOP

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8122019 Bishop 1997








910 BISHOP

8122019 Bishop 1997










8122019 Bishop 1997


8122019 Bishop 1997









8122019 Bishop 1997







914 BISHOP

8122019 Bishop 1997







8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


REFERENCES
























920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

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8122019 Bishop 1997









908 BISHOP

8122019 Bishop 1997






8122019 Bishop 1997








910 BISHOP

8122019 Bishop 1997










8122019 Bishop 1997


8122019 Bishop 1997









8122019 Bishop 1997







914 BISHOP

8122019 Bishop 1997







8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


REFERENCES
























920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

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8122019 Bishop 1997








910 BISHOP

8122019 Bishop 1997










8122019 Bishop 1997


8122019 Bishop 1997









8122019 Bishop 1997







914 BISHOP

8122019 Bishop 1997







8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


REFERENCES
























920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

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8122019 Bishop 1997








910 BISHOP

8122019 Bishop 1997










8122019 Bishop 1997


8122019 Bishop 1997









8122019 Bishop 1997







914 BISHOP

8122019 Bishop 1997







8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


REFERENCES
























920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

29 _










8122019 Bishop 1997










8122019 Bishop 1997


8122019 Bishop 1997









8122019 Bishop 1997







914 BISHOP

8122019 Bishop 1997







8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


REFERENCES
























920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

29 _










8122019 Bishop 1997


8122019 Bishop 1997









8122019 Bishop 1997







914 BISHOP

8122019 Bishop 1997







8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


REFERENCES
























920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

29 _










8122019 Bishop 1997









8122019 Bishop 1997







914 BISHOP

8122019 Bishop 1997







8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


REFERENCES
























920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

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8122019 Bishop 1997







914 BISHOP

8122019 Bishop 1997







8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


REFERENCES
























920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

29 _










8122019 Bishop 1997







8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


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920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






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621 _





















922 BISHOP

8122019 Bishop 1997






51

29 _










8122019 Bishop 1997













916 BISHOP

8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


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920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

29 _










8122019 Bishop 1997











8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


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920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

29 _










8122019 Bishop 1997










918 BISHOP

8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


REFERENCES
























920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

29 _










8122019 Bishop 1997




Conclusion





8122019 Bishop 1997


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920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






6

621 _





















922 BISHOP

8122019 Bishop 1997






51

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920 BISHOP

8122019 Bishop 1997



























8122019 Bishop 1997






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8122019 Bishop 1997






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8122019 Bishop 1997






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8122019 Bishop 1997






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8122019 Bishop 1997






51

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Documents

Bishop 1997