Haskins Laboratories Status Report on Speech Research1990, SR-101 /102,85-100

Phonological Ambiguity and Lexical Ambiguity: Effects onVisual and Auditory Word Recognition*

Ram Frost,t Laurie B. Feldman,tt and Leonard Katzttt

The present study was concerned with the relative effects of phonological ambiguity andlexical ambiguity on word recognition. The study exploited a special property of Serbo­Croatian. Specifically, readers of that language are familiar with two alphabets whichshare a subset ofletters that have two different pronunciations, one in each alphabet. Thestimuli in this study used letter strings that could be pronounced differently in eachalphabet. Some of these strings had two different meanings, one for each pronunciation;for others, only one of the two pronunciations was meaningful. In three experiments,subjects were presented with an ambiguous printed word and, simultaneously, with aspoken word and were required to determine if they matched. The spoken words werepresented clearly or degraded by noise. The speed of matching the spoken words tophonologically ambiguous letter strings was measured relative to their phonologicallyunequivocal controls. The results indicated that phonological ambiguity slowed stimulusmatching. Moreover, phonological ambiguity had a greater effect when the phonologicallyambiguous form represented two meaningful words. In neither simultaneous nor delayedpresentation did auditory degradation interact with phonological or lexical ambiguity,suggesting that perception of the spoken word was independent from perception of theprinted word.

In the past decade, the problem of lexicalambiguity has attracted the attention of manyresearchers concerned with models of printedword recognition. Since lexical ambiguity exists inmany languages, an examination of the process ofdisambiguation may clarify the relation betweenorthography and phonology in the mental lexicon.

Ambiguity can exist in the relationships be­tween the orthographic and phonological forms ofa word, or between the phonological form and itssemantic representation. The printed word"bank," for example, has one pronunciation (andtherefore an unambiguous phonological represen­tation), but two meanings. In contrast to"bank,"

This work was supported in part by National Institute ofChild Health and Human Development Grant HD-01994 toHaskins Laboratories. We are indebted to Georgije Lukatela,Aleksandar Kostic, and the other members of the Laboratoryfor Experimental Psychology at the University of Belgrade, fortheir help, and to Shlomo Bentin, Keith Rayner, CharlesPerfetti, and two anonymous reviewers, for their criticism onearlier drafts of this paper.

85

the printed word "wind" has two differentphonological representations (lwindJ and /wayndJ)each of which has a different semantic meaning. Ifwe consider a word to be, first of all, a phonologicalstructure, and the word's phonological repre­sentation to be its lexical entry, then the printedform "wind" has two lexical entries, each of whichis semantically differentiated. Resolving thephonological ambiguity necessarily designates onespecific lexical entry which, in turn, automaticallydisambiguates the semantic representation (andvice versa). The upper portion of Figure 1diagrams these relationships for English.

Effects of semantic ambiguity on visual wordrecognition have been demonstrated in severalstudies (for a review see Simpson, 1984).Rubenstein, Lewis, and Rubenstein (1971) showedthat lexical decisions are faster for homographslike "bank," than for nonhomographic words. Theexplanation for this effect was that words withmultiple meanings have multiple lexical entries,and therefore the probability of encountering oneof them is greater than the probability of detecting

86 Frost et al.

a single entry (see also Jastrembsky, 1981).Effects of phonological ambiguity were demon­strated in the naming task which, by its nature,requires a fully specified phonological form. Homo­graphs like "wind" which are phonologicallyambiguous, take longer to name than homographswith a single pronunciation (Kroll & Schweickert,1978).

An additional source of phonological ambiguitycan be demonstrated in languages with twodistinct and equivalent orthographies like Serbo­Croatian. In Serbo-Croatian, the Roman and theCyrillic alphabets are both taught to allelementary school children, and used interchange­ably by the skilled reader. Most characters in thetwo alphabets are unique to one alphabet or theother, but there are some characters that occur inboth. Of those, some receive the same phonemicinterpretation regardless of alphabet (COMMONletters), but others receive a differentinterpretation in each alphabet (AMBIGUOUSletters). Letter strings that include unique letterscan be pronounced in only one alphabet. Similarly,letter strings composed exclusively of commonletters can be pronounced in the same manner inboth alphabets. In contrast, strings that containonly AMBIGUOUS and COMMON letters arePHONOLOGICALLY BIVALENT. They can bepronounced in one way by treating the charactersas Roman letters, and in a distinctly different wayby treating them as Cyrillic letters. For example,the letter string "POTOP" can be pronounced asIpotopl if the ambiguous character P is interpretedaccording to its Roman pronunciation. Bycontrast, if the letter string is taken as a Cyrillicspelling, the grapheme P receives the pronun­ciation Irl and the string must be pronouncedIrotorl (the characters 0 and T are common, andhave the same pronunciation in the twoalphabets). In the case of POTOP, both pronun­ciations are legal Serbo-Croatian words (theformer means "flood" and the latter, "rotor").

When a phonologically bivalent word of Serbo­Croatian is read in isolation, the alphabet is notspecified by a context and, therefore, the spelledform can be pronounced in two different ways.Two types of such bivalent strings exist. In one ofthese, both pronunciations are known to thereader as words (Le., have lexical entries). Suchletter strings are both phonologically and lexicallyambiguous. In the other type, which occurs morefrequently, only one ofthe two pronunciations is aword, while the other is a nonword. Such stringsare phonologically ambiguous, but since they arerelated to only one lexical entry they are not

lexically ambiguous. An illustration of the variousforms of ambiguity in Serbo-Croatian is presentedon the lower portion of Figure 1.

In the present study we exploited the bi­alphabetical property of Serbo-Croatian, in orderto assess the relative contributions of phonologicaland lexical ambiguity to interference in theprocess of word recognition. Specifically, our aimwas to investigate whether there are conditionsunder which phonological ambiguity in theabsence oflexical ambiguity is sufficient to impairperformance, or whether lexical ambiguity is anecessary condition for such interference, whenwords are presented in isolation. This issue mayhave relevance, at least to some extent, toorthographies which represent phonology in anindirect manner (Le., printed letter strings can beread in more than one way). It focuses on whetherphonologically ambiguous letter strings areprocessed differently regardless of the lexicalstatus of the possible pronunciations.

Previous studies in Serbo-Croatian examinedhow fluent bi-alphabetic readers processambiguous print. Lukatela, Popadic, Ognjenovic,and Turvey (1980), investigated lexical decisionperformance in Serbo-Croatian, comparingphonologically ambiguous and unequivocal words.They demonstrated that words that could bepronounced in two different ways were acceptedmore slowly as words, relative to words that couldbe read in only one way. Similar results werefound by Feldman and Turvey (1983) whocompared phonologically ambiguous and phono­logically unequivocal forms of the same lexicalitems. This outcome was interpreted to suggestthat, in contrast to English, lexical decisions inSerbo-Croatian are necessarily based on theextraction of phonology from print (Turvey,Feldman, & Lukatela, 1984).

The relative contributions of phonological andlexical factors were not directly assessed in theseprevious studies. However, although Lukatela etal. (1980) demonstrated that phonologically am­biguous letter strings incurred longer lexical de­cision latencies than phonologically unequivocalstrings, they did not find a significant difference indecision latencies between ambiguous strings withone or with two lexical entries. In fact, phonologi­cally bivalent letter strings slowed subjects re­sponses (although to a lesser extent), even if thetwo possible readings of the letter strings repre­sented two nonwords (see also Lukatela, Savic,Gligorijevic, Ognjenovic, & Turvey, 1978).Interestingly, words that were composed exclu­sively of COMMON letters which were alphabeti-

Phonological Ambiguity and Lexical Ambiguity: Effects on Visual and Auditory Word Recognition 87

cally bivalent but phonologically unequivocal, didnot slow lexical decisions, relative to their uniquealphabet controls (Feldman & Turvey, 1983).Finally, the magnitude of the difference in deci­sion latencies to bivalent and unequivocal forms ofa word varied with the number of ambiguous let­ters in the bivalent form of that word (Feldman,

Kostic, Lukatela, & Turvey, 1983; Feldman &Turvey, 1983). In general, these results suggestedthat the reader of Serbo-Croatian processes printby a phonologically analytic strategy, that pre­cedes lexical access. Consequently, as a rule, hisor her performance is hindered by phonologicalambiguity. (See Feldman (1987), for a review).

SEMANTICREPRESENTATION

PHONOLOGICLEXICON

ORTHOGRAPHICSTRUCTURE

"BANKMONEY"

SEMANTICREPRESENTATION "FLOOD"

ENGLISH

"WIND""ROTOR"

PHONOLOGICLEXICON

ORTHOGRAPHICSTRUCTURE

SERSO-CROATIAN

Figure 1. Different types of ambiguity in English and in Serbo-Croatian.

88 Frost et al.

However, the conclusion that the phonologicallyanalytic Serbo-Croatian reader is not sensitive tothe lexical status of the different alphabeticreadings may be premature. All of the abovestudies monitored either lexical decisions ornaming of isolated words. These tasks may nothave been sensitive enough to detect lexicaleffects. In particular, they may not have detecteddifferences in the processing of phonologicallyambiguous letter strings which represented one ascontrasted with two words. Lexical decisions ofisolated words can be made on a fast familiarityjudgment (whether visual or phonological), that isbased on a pre-lexical superficial recognitionprocess, not necessarily involving lexical access(see Balota & Chumbley, 1984, 1985, for adiscussion of this point). In contrast to lexicaldecision, the naming task may require a deeperphonological processing, but it does notnecessarily reveal whether an alternative word,other than the reader's final choice, had beenconsidered during the process of phonologicaldisambiguation.

In a recent study Lukatela, Turvey, Feldman,Carello, and Katz (1989), examined whether apresentation of semantic context can override anambiguous alphabetic context. They have shownthat the correct and consistent alphabeticassignment for a letter string can indeed be offsetby previously accessed lexical entries, (that areactivated by semantic information). Hence, incontrast to the previous conclusions of Turvey etaI. (1984), who suggested that a pre-lexicalphonological analysis of print is mandatory inSerbo-Croatian, these results demonstrate thatthe Serbo-Croatian reader can also be affected bythe lexical characteristics of the printed stimulus,if the experimental conditions invite deeperprocessing. For the purpose of the present study,in order to assess the relative effects of lexical andphonological ambiguity on the process of wordrecognition, we needed a methodology that tappedmore directly the process of mapping printedwords into lexical phonological structures.Therefore, in the present experiments weemployed the "matching task" which was used insome of our previous studies for a similar purpose(Frost & Katz, 1989, Frost, Repp, & Katz, 1988).

The matching taskIn the matching task subjects are

simultaneously presented with a printed word (ora nonword) on a computer screen, and with aspoken word (or a nonword) via headphones. Thesubject is asked to decide as fast as possible

whether or not the stimuli presented in the visualand the auditory modalities are the same (positiveresponse); or whether they are different (negativeresponse). Our assumption is that thesimultaneous presentation of visual and auditorywords produces separate activations of theorthographic and the phonologic lexical systems,that are, at least, initially independent. In orderto match the spoken and the printed forms ofwords, they both have to be represented on thesame metric, that is to converge at an identicallexical entry. Theoretically, this entry can beeither phonologic or orthographic. Thus, thematching of a spoken and a printed word can beachieved, either by recoding the print into aphonological representation, and by comparing itto the phonological representation derived by theauditory channel, or, alternatively, by recodingthe spoken form into an orthographic code and bycomparing it to the printed word. However, thesetwo theoretical possibilities are not equallyprobable. The transformation of speech into anorthographic representation is, by far, lesspracticed than the transformation of spelling intophonology. Indeed, in a previous study whichinvolved simultaneous presentation of print andspeech, we have demonstrated that it is theprinted word which is transformed into a detailedphonetic representation, and that this process isvery fast and automatic (Frost et aI., 1988).Consequently, we assume that the common endresult of both print and speech processing in thematching task is a phonological representation inthe lexicon. The claim that the phonologicalrepresentation is indeed lexical, is supported byresults in a previous study that used the matchingtask (in English and Serbo-Croatian), in whichword frequency effects were demonstrated, anddifferences were found between words andpseudowords (Frost & Katz, 1989).

The matching of an orthographic form to aspoken word might be performed in at least twodifferent ways. One is to construct, at a first stage,functionally independent and complete phono­logical representations of the printed word andthe spoken stimulus. These two representationsare further compared at a subsequent stage. Thispossibility is in accordance with Morton's separateauditory and visual input logogens (Morton, 1981).A second possibility is that the process of mappingthe print into phonology and the process ofmapping the spoken stimulus into the commonphonological structure are weakly interactive.According to this alternative, the two processesshare information before completing their

Phonological Ambiguity and Lexical Ambiguity: Effects on Visual and Auditory Word Recognition 89

respective analyses, and by doing so, alter theextent of each other's processing. Thus, seeingprint and forming a partial phonological represen­tation of it can confirm (or contradict) a match tothe accumulating phonological information beingreceived via speech. In a complementary way, therapid accumulation of information about whichphonemes could be represented by the print canbe influenced by the phonological information thatis being received simultaneously via the auditorychannel. Consistent with the interactive view areresults that show reduced but significant cross­modal priming of auditory recognition of printedwords (Hanson, 1980; Kirsner, Milech, & Standen;1983), and visual-auditory interference in a Stroopparadigm in the naming task (Tanenhaus,Flanigan, & Seidenberg, 1980). It is important todistinguish between these two alternativepossibilities in order to understand how phonologyis derived from print.

In the three experiments reported here, subjectswere presented with printed and spoken words,and were required to determine whether they areequivalent. The printed words were selected forthe matching task so that in their printed formthey were phonologically ambiguous in onecondition (e.g., "POTOP"), and unequivocal inanother condition (an unambiguous form of thesame word, e.g., "ROTOR," "nOTOn"). The spokenforms of the words presented auditorily werealways (necessarily) unambiguous, (e.g., /rotorl).Our primary aim was to determine the effects ofphonological and lexical ambiguity. Ifphonologicalambiguity in itself, affects the process of wordrecognition, then the efficiency of the matchingprocess should be directly influenced by thenumber of possible pronunciations for the printedword, regardless of the lexical status of thedifferent pronunciations. If lexical ambiguity(whether a letter string has two meaningfulpronunciations or only one) affects the matchingprocess, then subjects' performance forphonologically ambiguous strings that aremeaningful in both their Cyrillic and theirRoman forms, should be slower thanphonologically ambiguous strings that aremeaningful in only one alphabet. In bothinstances, performance will be assessed bycomputing the difference between latencies formatching the spoken words to the bivalent andunequivocal printed forms of the same word. Anadditional aim of the present study was toexamine the sequence of the early stages of thematching process. Hence, we introduced an

additional experimental manipulation whichconsisted of slowing the process of generatingphonological information from speech bydegrading the spoken presentation.

EXPERIMENT 1In Experiment 1 we presented. subjects with

phonologically bivalent letter strings that could beread as a word or as a nonword, and with bivalentstrings that could be read as two legal words (theformer strings were phonologically but notlexically ambiguous, while the latter were am­biguous at both the phonological and the lexicallevel). In the present experiment, when a lexicallyambiguous letter string was presented in print, itshigh-frequency (dominant) reading was alwayspresented auditorily as the matching referent.Similarly, the dominant alternative was alwaysdepicted when the unequivocal printed form of thesame letter string appeared. The purpose of theexperiment was to investigate whether lexicalambiguity is indeed perceived and affects thereader's performance even when the dominantreading of the bivalent letter string is presented.

A second aim of the present study was toinvestigate the time course of processing theprinted and the spoken word, by examining theinteraction of auditory degradation withphonological and lexical ambiguity. If the subjectderives the phonological representation of theauditory input independently of informationcoming from the visual channel, then the effect ofauditory degradation should be equivalent when'the printed stimulus is phonologically ambiguousand when it is not; in other words, the effects ofdegradation and ambiguity should be additive.Auditory degradation will slow the process ofretrieving the phonological structure from thephonetic input, but this reduction in the amountof phonological information will have no effect onthe generation of phonology from the print. On theother hand, if the partial phonemic informationarriving on the auditory channel facilitates theselection of a phonemic value for those graphemesthat are phonologically ambiguous (before thespoken word is fully analyzed), then the effects ofdegradation and phonological ambiguity shouldinteract: The matching of letters to theirrespective phonemes will be slower for thephonologically ambiguous letters than for theunequivocal letters (see Frost and Katz (1989);Frost, Repp, and Katz (1988) for a discussion ofthe simultaneous presentation with degradationtechnique).

90 Frost et ai.

MethodSubjects

Forty undergraduate students from theUniversity of Belgrade, all native speakers ofSerbo-Croatian, participated in the experiment forcourse credit.

Stimuli and DesignA total of 120 pairs of words were used in the

experiment. A pair consisted of a visual and anauditory presentation of a word. In sixty pairs, theprinted and the spoken words were the same, andin sixty pairs they were different. The 60 "same"pairs included our target words, while the 60"different" pairs were introduced as fillers in orderto achieve a probability of 0.5 for a "same"response.

The printed words were presented in Cyrillic orRoman characters, and appeared either in aphonologically bivalent form or in a phonologicallyunequivocal form. Of the phonologically bivalenttarget words, 20 had two meaningful pronun­ciations, one in each alphabet (usually belongingto the same syntactic class), and 20 had only onemeaningful pronunciation, half Roman and halfCyrillic, the other being a nonword. In additionthere were 10 unequivocal fillers in each alphabet.In summary, the Roman and the Cyrillic scriptswere mixed equally in all experimental conditions.

Obviously, the auditory form was always phono­logically unequivocal. For the lexically ambiguousletter strings (i.e., those that had two possiblemeaningful pronunciations), the spoken form wasalways the higher-frequency (dominant) lexical al­ternative. Since there is no standard frequencycount in Serbo-Croatian, the relative frequenciesof the two pronunciations were assessed by 30 na­tive' speakers. They were presented with thephonologically unequivocal printed forms of thehigh- and the low-frequency alternatives, andwere requested to decide for each pair which al­ternative was more frequent. Based on this judg­ing procedure, we selected 20 ambiguous words forwhich there was at least 75% agreement acrossjudges on which alternative was the dominant

meaning. Thus, the auditory stimulus alwaysmatched the higher frequency alternative of theprinted bivalent word. For the phonologically biva­lent but lexically unequivocal letter strings, thespoken form always was the lexical (meaningful)alternative, and not the nonword. The experimen­tal design is summarized in Table l.

Mismatched trials were constructed by pairingtwo words with the same length, and vowel­consonant structure, but which differed withrespect to one or two phonemes. The position ofthe nonidentical segments was distributed acrosswords uniformly. Half of the visually presentedtrials were in Roman and half in Cyrillic. Auditorydegradation was introduced in the experiment asan additional factor. Each subject heard an equalnumber of degraded and undegraded stimuli, andthis condition was counterbalanced acrosssubjects.

Four test lists were created each containing allfour combinations of ambiguity and degradation:For each subject, a word could appear in either itsphonologically ambiguous form or its unequivocalform with an auditory version that either was orwas not degraded by noise. Each test listcontained all four combinations of different items,and across lists a given word appeared in each ofthe four conditions. Each subject was tested withonly one list. This design allowed us first, tocompare the effects of phonological ambiguity (oneor two possible pronunciations), to the effects oflexical ambiguity (one or two meaningfulpronunciations of the printed word), and second,to examine whether auditory degradationinteracted with either phonological ambiguity orlexical ambiguity.

The visual stimuli were presented on aMacintosh computer screen. They subtended avisual angle of approximately 2.5 degrees onaverage. The auditory stimuli were originallyspoken by a male native speaker in an acousticallyshielded booth and recorded on an Otari MX5050tape-recorder. The speech was digitized at a20 kHz sampling rate. Each digitized stimuluswas edited using a digital waveform editor.

Table. 1. Examples ofwords in each experimental condition. Note, that the Roman reading ofBErAP is Ibetapl whichis a nonword. In contrast the Cyrillic reading ofPOTOP is Irotorl which is indeed a word.

ONE MEANINGFUL PRONUNCIATION TWO MEANINGFUL PRONUNCIAnONS

Unequivocal BivalentPrint Print

VEfAR BETAP

AuditoryStimulus

/vetar/

Unequivocalprint

nOTon

BivalentPrint

POTOP

AuditoryStimulus

/potop/

Phonological Ambiguity and Lexical Ambiguity: Effects on Visual and Auditory Word Recognition 91

Its onset was determined visually on an. oscilloscope, and was verified auditorily throughheadphones. A mark tone was then inserted, atthe onset of each stimulus. The digitized editedstimuli were recorded at three-second intervals ona two track audiotape, one track contained thespoken words while the other track contained themark tones. The purpose of the mark tone was totrigger the presentation ofthe printed word on thecomputer screen.

Auditory degradation was achieved by maskingeach spoken stimulus with signal-correlatednoise-that is, white noise with the same ampli­tude envelope as the spoken stimulus (Schroeder,1968). Speech and noise were added digitally inproportions of 0.3 and 0.7, corresponding to aconstant signal-to-noise ratio of -7.5 dB. The use ofsignal-correlated noise insured that thecharacteristics of the auditory degradation wereequivalent for all of the stimuli.Procedure and apparatus

Subjects wore headphones and sat in a semi­darkened room in front of the computer screen.The experimental task consisted of pressing a"Same" key if the visual and the auditory stimuliwere the same word, and pressing a "Different"key if they were different. The dominant hand wasalways used for the"yes" response.

The audiotape containing the verbal stimuli andthe mark tones was played on a two channel Sonytape recorder. The verbal stimuli were trans­mitted binaurally to the subject's headphones. Themark tones were transmitted through an interfaceto the Macintosh, where they triggered the visualpresentation and the computer's clock for reactiontime (RT) measurements. The experimentalsession began with 16 practice pairs. After thepractice, all 120 test trials were presented in oneblock.

Results and DiscussionMeans and standard deviations of RTs for

correct responses were calculated for each subjectin each of the experimental conditions. Withineach subject-condition combination, outliers thatwere greater than two standard deviations fromthe mean were eliminated. Outliers accounted forless then five percent of all responses. Thisprocedure was repeated in all three experimentsof the present study.

For the sake of clarity we will hereby define thevarious effects which were assessed in ouranalyses. 1) The main effect of phonological ambi­guity was measured by comparing RTs to wordswhich were presented in their bivalent alphabet,

with RTs to the same words when presented intheir unequivocal alphabet. 2) The main effect oflexical ambiguity reflects differing decisionlatencies to words which have two meaningfulpronunciations in their bivalent form, and wordswhich have only one meaningful pronunciation.Note that this main effect is difficult to interpret,since we are dealing here with two groups ofwords which differ in their respective frequencies.We will, therefore, ignore this main effect in ourfollowing analyses. A more meaningfulcomparison is 3) the interaction of lexicalambiguity, defined in terms of number ofmeanings, and phonological ambiguity, assessedin terms of the difference between bivalent andunequivocal forms. This interaction would suggestthat phonological ambiguity is indeed moredetrimental for words which have two meaningfulpronunciations than for words which have onlyone. 4) The main effect of degradation reflects thedifferent RTs for degraded and undegradedauditory stimuli. This main effect is, in fact,trivial. Of more interest is 5) the interaction ofdegradation with phonologica:! ambiguity andlexical ambiguity.

RTs in the different experimental conditions aresummarized in Table 2. Overall, RT was slowerwhen words were printed in their phonologicallyambiguous form than in their unequivocal form.Moreover, the difference between ambiguous andunequivocal forms appeared to be larger when thebivalent words had two meaningful pronun­ciations, rather than one. Finally, the effects ofauditory degradation were quite similar in allexperimental conditions.

To assess the statistical significance of thesetrends we performed an analysis of varianceacross subjects (F1) and across stimuli (F2), withthe main factors of phonological ambiguity(unequivocal or phonologically bivalent print),lexical ambiguity (one meaningful pronunciationor two), and degradation (normal or degradedpresentation). The main effects of phonologicalambiguity and degradation were significant: F1(1,39) =61.3, MSe =164,054, p < 0.001; F2 (1,19)= 26.2, MSe = 96,485, p < 0.001 and F1 (1,39) =20.7, MSe = 234,155, p < 0.001; F2 (1,19) = 18.2,MSe = 87,701, p < 0.001, respectively. Theinteraction of lexical ambiguity and phonologicalambiguity was marginally significant: F1(1,39) =3.07, MSe =207,802, p < 0.08; F2 (1,19) =2.05,MSe = 138,633, p < 0.1. The effect of degradationdid not interact with either print or lexicalambiguity (F1, F2 < 1.0). The three wayinteraction was also nonsignificant (F1, F2 < 1.0).

92 Frost et al.

Table 2. Matching RTs (in ms) and Errors (in parenthesis) for words printed in unequivocal or bivalent print. undernormal or degraded auditory presentations. Bivalent words had either one or two lexical entries in their bivalentforms. The dominant alternative was presented auditorily.

ONE MEANINGFUL PRONUNCIATION TWO MEANINGFUL PRONUNCIATIONS

Unequivocal Bivalent Bivalence Unequivocal Bivalent BivalencePrint Print Effect print Print Effect

Normal 740 787 47 707 778 71

(4%) (5%) (5%) (12%)

Degraded 780 817 37 751 823 72

(8%) (7%) (11%) (17%)

We analyzed the percentage of errors in aseparate analysis of variance. The results aresimilar to the RT analysis and are presented inTable 2. The main effects of phonologicalambiguity and degradation were significant:Fl(1,39) = 3.6, MSe = 24.6, p < 0.06; F2 (1,19) =5.10, MSe = 17.5, p < 0.03; and F1(1,39) =11.0,MSe = 12.0, p< 0.001; F2(1,19) = 8.65, MSe =10.5,p < 0.008; respectively. The interaction ofphonological ambiguity and lexical ambiguity wasmarginally significant in the subject analysis,F1(1,39) = 3.40, MSe = 26.1, p < 0.07, but highlysignificant in the stimuli analysis, F2 (1,19) =8.65, MSe = 13.6, p < 0.008. Again, degradationdid not interact with the other factors.

Although the results were not fully consistent,they suggest that phonological ambiguity affectedword recognition: If a letter string could bepronounced in two ways, subjects' performancewas slowed, even when only one of thosepronunciations was a real word. It is important toemphasize that because the unequivocal andambiguous forms were related to the same word,differences between these two forms cannot berelated to differences in their relative frequency. Ifanything, the cumulative frequency for thebivalent form was higher than for the unequivocalform (see also Feldman et al., 1983). The effect ofphonological ambiguity appeared to be even largerwhen the ambiguous printed stimulus could havebeen read as two meaningful words than when itcould be read in only one meaningful way.However, this interaction was more pronounced inthe error analysis.

The effects of auditory degradation provideadditional insights concerning the interaction of

the visual and the auditory systems in wordrecognition. Clearly, auditory degradation of thespoken stimulus resulted in an overall slowing ofsubjects' responses. However, this effect wasadditive, and did not interact with phonological orlexical ambiguity. This result suggests that, atleast in the processing of high-frequency words,the extraction of phonemic information from theauditory signal is performed independently of thevisually-based processing of the words presentedin print. In Experiment 2, we determine if thisoutcome can be generalized to the perception ofthe low-frequency alternative reading of bivalentwords.

EXPERIMENT 2The effects of lexical ambiguity revealed in

Experiment 1 may have been attenuated becauseonly the high-frequency lexical alternative of aphonologically bivalent word was presented to thesubject. It is possible that when the lexicalalternatives of a bivalent letter string arediscrepant in frequency, only the dominant alter­native is activated sufficiently, and thereforelexical ambiguity does not have a strong effect onthe process of word recognition. This could haveresulted in a considerable reduction of theambiguity effect, thereby attenuating the inter­action between phonological ambiguity and lexicalambiguity observed in Experiment 1.

Our aim in Experiment 2 was to examine theeffect of phonological ambiguity and itsinteraction with lexical ambiguity and auditorydegradation when the low-frequency (subordinate)alternatives are presented as unequivocalcontrols.

Phonologiall Ambiguity and Lexiall Ambiguity: Effects on Visual and Auditory Word Recognition 93

MethodSubjects

Forty undergraduate students from theUniversity of Belgrade, all native speakers ofSerbo-Croatian, participated in the experiment forcredit. None of them had participated inExperiment 1.Stimuli and Design

The stimuli, design, procedure, and apparatuswere identical to those used in Experiment 1,except that when the bivalent words had twomeaningful pronunciations, the low-frequencymeaning was presented auditorily as thematching referent, and as the unequivocal printedcontrol.

Results and DiscussionRTs and errors in the different experimental

conditions are summarized in Table 3. As inExperiment 1, we performed an analysis of vari­ance across subjects (F1) and across stimuli (F2),to assess the relative effects of phonologicalambiguity, lexical ambiguity, and auditorydegradation.

The main effects of phonological ambiguity andauditory degradation were .significant: F1(1,39) =115, MSe = 295,386, p < 0.001, F2 (1,19) = 96.3,MSe = 74,130, p < 0.001; F1(1,39) = 37.7, MSe =258,479, p < 0.001, F2 (1,19) = 8.44, MSe =286,057, p < 0.01, respectively. The interaction ofphonological ambiguity and lexical ambiguity washighly significant: F1(1,39) = 55.2, MSe = 145,027,p < 0.001, F2 (1,19) = 18.1, MSe = 94,976, p <0.001. Finally, as in Experiment 1, degradationdid not interact either with phonological ambi­guity (F1, F2 < 1), or with lexical ambiguity (F1<1.0, F2 = 1.6).

Similar results were obtained in the erroranalysis. There was a significant main effect ofphonological ambiguity, F1(1,39) = 28.2, MSe =

9.1, p < 0.001, F2(1,19) = 13.0, MSe = 7.0. p <0.001, and auditory degradation, Fl(1,39) = 23.5,MSe = 7.8,p < 0.001, F2 (1,19) = 20.7, MSe = 10.0,p < 0.001. There was a significant interaction ofphonological ambiguity and lexical ambiguityF1(1,39)= 4.87, MSe = 10.0, P < 0.03. Degradationdid not interact with phonological ambiguity (F1 <1.0, F2 =1.97), or with lexical ambiguity F1 (1,39)= 3.5, MSe = 16.8, p < 0.07, F2 (1,19) < 1.0, MSe=9.7,p < 0.4).

Thus, the trends revealed in Experiment 1 werereplicated in Experiment 2, but the differenceswere strongly enhanced. The effect of phonologicalambiguity was three times larger for words thathad two meaningful pronunciations, than forwords with only one. When this interaction iscompared to the one obtained in Experiment 1, itis clear that the major difference occurs for stimulithat could be read as two legal words. Here, theeffect of phonological ambiguity was twice as largeas in Experiment 1 (approximately 140 ms, ascompared to 70 ms in the previous experiment).The statistical significance of this difference wasassessed by using a mixed model ANOVA design,with the additional between-subjects factor offrequency. The three-way interaction of phonolog­ical ambiguity, lexical ambiguity, and frequency,was indeed significant F1(1,78) = 11.7, MSe =4523, p < 0.001.

In spite of the enhanced effects of phonologicalambiguity and its interaction with lexicalambiguity, it is clear that the effect of auditorydegradation was similar for phonologically biva­lent strings with one and two meaningfulpronunciations, and for phonologically unequiv­ocal words. This pattern was revealed in both theRT and error analyses and was, in fact, verysimilar to the pattern obtained in Experiment 1.This outcome is consistent with our claim that theprocessing of the degraded auditory informationwas completed independently of the visual input.

Table 3. RTs (in ms) and Errors (in parenthesis) when the subordinate alternative was presented auditorily.

ONE MEANINGFUL PRONUNCIATION TWO MEANINGFUL PRONUNCIATIONS

Unequivocal Bivalent Bivalence Unequivocal Bivalent BivalencePrint Print Effect· print Print Effect

Normal 749 801 52 749 894 145

(1%) (3%) (10%) (14%)

Degraded 808 850 42 818 970 152

(5%) (10%) (13%) (25%)

94 Frost et al.

Our results seem to suggest that a phonologicallybivalent letter string was first recoded as (oractivated) its dominant phonological alternativewhich was then compared to the spoken word.Since, in the present experiment, the spoken wordrepresented the subordinate alternative, thesubject would first find a mismatch and only thenwould generate the less frequent alternative. Thistendency might explain the poorer overallperformance in the present experiment.

EXPERIMENT 3In both Experiments 1 and 2, we found that the

degradation of the auditory input did not interactwith phonological ambiguity or with lexicalambiguity. These results lead us to conclude thatsubjects constructed complete phonologicalrepresentations of the printed and the spokenstimuli, independently of each other. It is possible,however, that this outcome resulted from differenttime courses of lexical activation caused by theprinted and the spoken words. Although theonsets of the visual and auditory presentationswere simultaneous, all of the print informationwas available immediately, while the auditoryinformation that constituted the spoken word wasdistributed over 400 to 500 ms of time. Thus, inExperiments 1 and 2, the auditory informationeffectively lagged behind the visual information.This basic difference between auditory and visualpresentation could have caused the subject toprocess the print first and the speech subse­quently and independently. A similar argumentwas proposed by Glucksberg, Kreuz, and Rho(1986), who suggested that in a cross-modalbackward priming paradigm, a visual target wordpresented after the onset of an auditory primeword might affect the lexical interpretation of theauditory stimulus. The purpose of Experiment 3was to investigate whether auditory degradationdid not interact with phonological ambiguitybecause of the particular timing relation betweenvisual and auditory stimulus presentations, orwhether the outcome we observed indeed reflects amore general strategy for processing bi-modalverbal information.

In Experiment 3, the visual presentation wasdelayed by 200 ms, relative to the onset of thespoken word. (A lag of 200 ms is slightly shorterthan the average recognition point of a two­syllable word presented auditorily (e.g., MarslenWilson & Tyler, 1980). Thus, the printed word waspresented not at the onset of the spoken word, butduring its distributed presentation. If the subject

had the tendency, in the first two experiments, toprocess the print first, the new timing relationshould counteract this bias. As noted above, thepurpose of this manipulation was to encourageparallel processing of print and speech, in order toincrease the possibility of interactive processing.

MethodSubjects

Eighty undergraduate students from theUniversity of Belgrade, all native speakers ofSerbo-Croatian, participated in the experiment forcredit. None of the subjects participated in theprevious experiments. Forty of the 80 subjects(group A) were tested with the stimuli of Exper­iment 1 (dominant alternatives), and the other 40(group B) were tested with the stimuli employedin Experiment 2 (subordinate alternatives).

Stimuli, Design, and ProcedureThe stimuli, design, and apparatus were

identical to those used in Experiments 1 and 2.The procedure, however, differed in one importantrespect from the previous experiments: the visualpresentation of the stimuli lagged from the speechonset by 200 ms, and the frequency of the lexicalalternatives for spoken forms was manipulatedbetween sets of subjects.

Results and DiscussionRTs are summarized in Table 4. We conducted

separate analyses of variance for subjects whowere presented with the high-frequency spokenalternatives (Experiment 3a), and for subjects whowere presented with the low-frequency spokenalternatives (Experiment 3b). Each analysis wasperformed across subjects (F1) and across stimuli(F2), with the main factors of phonologicalambiguity, lexical ambiguity, and auditorydegradation.

For the group presented with the dominantalternatives (group A), the main effects ofphonological ambiguity and degradation weresignificant: F1 (1,39) =55.4, MSe =176,745, P <0.001, F2 (1,19) =20.7, MSe =128,627, P < 0.001,and F1 (1,39) =25.6, MSe =382,340, P < 0.001, F2(1,19) = 22.7, MSe = 121,110, P < 0.0010 Theinteraction of phonological ambiguity and lexicalambiguity was significant, F1 (1,39) = 13.1, MSe =170,770, P < 0.001, F2 (1,19) = 4.37, MSe =153,201, P < 0.05. More importantly, just as inExperiments 1 and 2, degradation did not interactwith lexical ambiguity, or with phonologicalambiguity (F1, F2 < 1.0).

Phonological Ambiguity and Lexical Ambiguity: Effects on Visual and Auditory Word Recognition 95

Table 4. RTs (in ms) and Errors (in parenthesis) when the onset of the dominant (3a) and the subordinate (3b)alternatives was presented auditorily before the visual form.

DOMINANTONE MEANINGFUL PRONUNCIATION TWO MEANINGFUL PRONUNCIATIONS

Unequivocal Bivalent Bivalence Unequivocal Bivalent BivalencePrint Print Effect print Print Effect

Normal 637 666 29 580 658 78

(1%) (1%) (6%) (9%)

Degraded 688 718 30 636 724 88

(13%) (11%) (14%) (22%)

SUBORDINATEONE MEANINGFUL PRONUNCIATION TWO MEANINGFUL PRONUNCIATIONS

Unequivocal Bivalent Bivalence Unequivocal Bivalent BivalencePrint Print Effect print Print Effect

Normal 615 652 37 621 713 92

(1%) (3%) (10%) (17%)

Degraded 688 723 35 700 781 81

(11%) (17%) (20%) (30%)

The error analysis revealed a significant effect ofauditory degradation, F1(1,39) = 40.0, MSe = 22.7,p < 0.001, F2 (1,19) = 46.7, MSe = 20.0, p < 0.001,and a significant interaction· of phonologicalambiguity and lexical ambiguity, F1(1,39) = 5.9,MSe = 12.9, p < 0.01, F2 (1,19) = 3.72, MSe = 20.8,p < 0.06. No interaction with degradation wasfound (F1, F2 < 1.0).

Similar results were obtained with theexperimental group presented with thesubordinate alternatives (group B): all maineffects were significant: F1(1,39) = 41.6, MSe =281,833, P < 0.001, F2 (1,19) = 17.3, MSe =165,043, p < 0.001; F1(1,39) =. 36.4, MSe =455,213, P < 0.001, F2 (1,19) = 38.7, MSe =118,930,p < 0.001; for phonological ambiguity andauditory degradation, respectively. Theinteraction of phonological ambiguity and lexicalambiguity was significant: Fl(1,39) = 7.93, MSe =251,528, p < 0.007, F2 (1,19) = 5.13, MSe = 84,984,p < 0.03. As in all previous experiments,degradation did not interact with eitherphonological ambiguity, (F1, F2 < 1.0), or withlexical ambiguity, (F1, F2 = 0.0), nor was thethird-order interaction significant (F1, F2 < 1.0).

The error analysis revealed only significantmain effects for phonological ambiguity, F1(1,39)= 28.9, MSe = 11.8, p < 0.001, F2 (1,19) = 5.53,MSe = 26.0, p < 0.02, lexical ambiguity, F1(1,39)=69.0, MSe =15.9, p < 0.001,F2 (1,19) = 5.1, MSe=35.7, p< 0.03, and auditory degradation, F1(1,39)= 45.6, MSe = 23.1, p < 0.001, F2 (1,19) = 35.2,MSe = 26.1, p < 0.001.

The results obtained in Experiment 3 are verysimilar to those obtained in Experiment 1 and 2.In general, delaying the printed information didnot interfere with subjects' performance. Similarerror rates were found for normal and delayedpresentation, and the faster RTs in the delayedcondition are, in fact, an artifact of delayedmeasurement onsets (In all experiments, RTswere measured from print onset). Regardless ofwhich phonological alternative was presentedauditorily, phonological ambiguity did affectsubjects' performance. Moreover, the effect, wasstronger when the phonologically ambiguouswords had two meaningful pronunciations thanwhen they had only one. If we consider first, theresults obtained with the dominant alternatives, itappears that our experimental manipulation

96 Frost et ai.

actually enhanced the interaction betweenphonological ambiguity and lexical ambiguity,obtained in Experiment 1. Whereas the statisticalsignificance of these trends was unclear inExperiment 1, Experiment 3a provides a reliableconfirmation of this observed effect. Even whenthe subject hears the dominant alternative of aphonologically bivalent word, both lexical (andphonological) interpretations are automaticallyactivated. Nevertheless, in spite of the enhancedeffect found in Experiment 3a, degradation stilldid not interact with either phonologicalambiguity or with lexical ambiguity. We conclude,again, that the two processes of generatingphonological representations from the visual andauditory input channels were independent.

The results obtained with the delayed visualpresentation of the subordinate alternatives(Experiment 3b), suggest that the effect ofphonological ambiguity for words with twomeaningful pronunciations was reduced relativeto the effect we found in Experiment 2. In order toassess the statistical significance of thisdifference, we conducted an analysis whichcompared directly the interaction of phonologicaland lexical ambiguity in Experiments 2 and 3b.We used a mixed ANOVA design with theadditional between subjects factor of lag. Theanalysis revealed that the three-way interaction ofphonological ambiguity, lexical ambiguity, andlag, was indeed significant (F(l,78) =5.1, MSe =5084, p < 0.02). This outcome provides additionalinsights concerning the effect of lagged visualpresentation on the disambiguation process. Wewill discuss this finding further in the GeneralDiscussion.

GENERAL DISCUSSIONThe present study was designed to examine the

effects of phonological ambiguity and lexicalambiguity in print on word recognition. In threeexperiments, we exploited a special property of theSerbo-Croatian language-its transcription toboth the Roman and Cyrillic alphabet-in order tomanipulate separately the phonological ambiguityof a printed word and the number of lexicalentries it represents. Our subjects were presentedsimultaneously with a printed and a spoken wordand were required to determine whether theywere the same or different. The speed and theaccuracy of matching the printed and the spokenforms were measured when the print had eitherone possible pronunciation or two, and if two,when both pronunciations were real words or onlyone was. In addition we examined whether

auditorily degrading the spoken word interactedwith either lexical or phonological ambiguity.

Across experiments, we manipulated thefrequency of the lexical alternatives representedby the phonologically bivalent word, as well as thetemporal interval between the onset of the speechand the print. A consistent pattern of resultsemerged throughout the study. First, both thenumber of possible pronunciations for a printedword and their lexical status affected wordrecognition. Second, these effects interacted:phonological ambiguity had a greater effect whenthe bivalent form could be read as two legal wordsthan when it could be read as only one. Third,auditory degradation never interacted either withprint ambiguity or with lexical ambiguity. Inaddition, these effects were obtained regardless ofthe lexical alternative's frequency or the temporalonset ofprint presentation.

Previous studies using the lexical decision taskexamined how fluent bi-alphabetic readers ofSerbo-Croatian process ambiguous print. Thesestudies showed that phonologically bivalent letterstrings, both words and nonwords, indeedincurred longer decision latencies than differentunequivocal strings. However, the effect ofphonological ambiguity was similar forphonologically bivalent letter strings whether thestring represented real words or nonwords(Lukatela et a1. 1978; 1980).1 In contrast to theseprevious studies, our results suggest that thereader is affected not only by the number ofpossible pronunciations of a printed word, but alsoby their lexical status. That is, print bivalencecaused greater difficulties when both of thepronunciations were attached to lexical entriesthan when only one pronunciation was a realword. One advantage of the design employed inthe present study is that it allowed us todemonstrate the relative contribution of lexicaland phonological factors, by comparing subjects'performance for the same word presented in eithera bivalent printed form or in an unequivocalprinted form. We found, in all three experiments,that the inhibitory effect on reaction time causedby bivalent print was roughly twice as large forbivalent strings with two lexical entries ascompared to bivalent strings with only one realword entry (the other pronunciation being anonword).

As noted above, the discrepancy in resultsbetween the present and previous studies may bedue to the different tasks that were employed. Thematching task explicitly requires matching theprinted and the spoken forms of a word. Effects of

Phonological Ambiguity and Lexical Ambiguity: Effects on Visual and Auditory Word Recognition 97

lexical ambiguity should arise whenever theprinted letter string is recoded into more than onephonological form. In this case two conflictingalternative representations will be matched withthe phonological representation derived from theauditory input which is necessarily unambiguous.In contrast, lexical decisions can be made on a fastfamiliarity judgment (Balota & Chumbley, 1984,1985), and naming can be performed by a selectionof only one lexical candidate. One consequence ofthe different task requirements is that lexicaldecision and naming can be performed success­fully on the basis of one complete representation.Therefore, our results seem to provide evidencethat the matching task is more sensitive than thelexical decision and naming tasks for detectingeffects of phonologically-derived lexical ambiguity.

A large effect of lexical status was obtained inthe present study: phonological ambiguityhindered performance to a greater extent whenboth pronunciations were meaningful than whenonly one pronunciation was a word. This effectsuggests that interference was caused by theconflict between the two lexical entries. Althoughlexical effects in phonological disambiguation havebeen demonstrated before in Serbo-Croatian, theywere studied only in a priming paradigm. That is,a prime that was either semantically oralphabetically related to one of the lexical entriescontributed to the disambiguation process(Feldman, 1987). Similarly, Lukatela et al. (1989)have shown that prior lexical access can overridethe consistent assignment of an alphabet readingin cases where the target letter string containedillegal combinations of Roman and Cyrillic letters.Our results with the matching task suggest thatlexical factors can also be demonstrated whenbivalent strings are presented in isolation.

The influence of frequency provides additionalinsights concerning the proce~sing of bivalentletter strings. When the subordinate alternativewas presented auditorily, it inhibited the responseto its matching but bivalent printed letter string:In Exp~riment 2 and 3B (which used the low­frequency spoken words), the difference betweenbivalent and unequivocal printed forms wasgreater than was the difference in Experiments 1and 3a. This outcome suggests that subjectsinitially access the dominant alternative related tothe bivalent printed string, and that a mismatchbetween its phonological form and the subordinateform presented on the auditory channel was thecause for the longer RTs (and greater number oferrors) encountered in these experimental conditi­ons. These results are parallel to meaning

frequency effects of homophonic homographsreported by Hogaboam and Perfetti (1975) and,overall, support frequency-ordered access modelsfor lexically ambiguous words (e.g., Simpson,1981; Simpson & Burgess, 1985).

In a task in which subjects had to find apolysemous word in a sentence, Hogaboam andPerfetti (1975) demonstrated that detection wasfaster when the context was related to thesubordinate meaning of the ambiguous word thanwhen it was related to the dominant meaning.Similar results have been recently reported byNeill, Hilliard, and Cooper (1988). In both studies,this outcome was interpreted to indicate that themore frequent or dominant meaning of ahomograph was retrieved at an initial stage.Because the initially activated dominant meaningdid not match the subordinate meaning which wassuggested by the context, ambiguity was easilydetected by the subjects. Evidence for thedifferential activation for high- and low~ frequencymeanings of ambiguous homographs was alsodemonstrated with event-related potentials (VanPetten & Kutas, 1987) and by monitoring eyemovements (Duffy,· Morris, & Rayner, 1988;Rayner & Frazier, 1989). These studies, however,examined the processing ofhomographs embeddedin context. More relevant to our study are theresults presented by Simpson and Burgess (1985)who examined the order of retrieving alternativemeanings of isolated homographs. In their study,Simpson and Burgess found that the priority foraccessing the alternative meanings, was deter­mined primarily by their relative frequencies: Themore frequent meaning was retrieved at an initialstage, and the subordinate meaning was activatedsubsequently. The above studies with Englishmaterials examined the time course of activationof homophonic homographs with two meaningsand a single pronunciation. Perhaps, the sameprinciple of frequency-ordered access can beextended to the materials in the present study:heterophonic homographs with two meanings andtwo pronunciations.

Note, however, that the effect of print bivalencewas obtained even when only the dominantmeaning was appropriate, and the subordinatemeaning was irrelevant (Experiments 1 and 3a).Even though the spoken word in these exper­iments was the dominant meaning, we still foundgreater effects of print bivalence for words withtwo lexical entries, over words with one lexicalentry. This result invalidates the possibility thatonly one meaning, the more frequent lexicalalternative, was generated from the bivalent letter

98 Frost et aI.

string. Rather, it suggests that the subordinatealternative was activated as well, even when thedominant alternative was presented auditorily asthe matching referent. The activation of thesubordinate alternative hindered subjects'performance for words with two lexical entriesbecause two lexical entries had to be consideredinstead of one.

In general, this outcome suggests exhaustiveaccess to all meanings of ambiguous words andthat these entries are automatically activated inthe process of word recognition (e.g., Onifer &Swinney, 1981; Seidenberg, Tanenhaus, Leiman,& Bienkowsky, 1982). Our results further supporta model in which both high- and low-frequencyalternatives are indeed activated but not inparallel; their order of activation is determined bytheir relative frequency, (Duffy et a1., 1988; Neillet. a1., 1988).

It appears that the Serbo-Croatian readerprocesses print in a phonologically analyticmanner. He/she is sensitive to the phonologicalambiguity presented by the orthographic struc­ture, and derives from it both phonological forms.Nevertheless, the dominant alternative usuallyhas an earlier or higher level of activation and,therefore, predominates over the subordinatealternative. However, this dominance effect can bereduced or reversed by priming the subordinatealternative of the print with the spoken(unambiguous) equivalent. This interpretation issupported by the effects of delaying the onset ofthe print in Experiment 3b.

In the delayed presentation of the subordinatewords, the ambiguity effect observed inExperiment 3b was reduced almost by halfrelative to the effect obtained in Experiment 2.This result demonstrates that the spoken wordwas at least partially analyzed before the bivalentword was presented. The partially perceivedsubordinate spoken word enhanced the level ofactivation of its lexical representation, effectivelypriming the subordinate lexical entry. Orderedaccess models assume different time courses ofactivation for the dominant and the subordinatealternatives of ambiguous words (e.g., Simpson &Burgess, 1985; Van Petten & Kutas, 1987).Simpson and Burgess (1985) have shown that thedominant meaning of a polysemous homographwas activated as soon as 16 ms from stimulusonset, whereas the subordinate meaning wasactivated only 100 ms from stimulus onset. Ourresults suggest that the partial presentation ofthespoken word prior to the printed stimulus

enhanced the activation of subordinate alter­natives which was triggered by the print, therebyreducing the frequency effect found in Experiment3b by half, relative to Experiment 2. However, the200 ms by which the auditory informationpreceded the visual information did notcompletely resolve the printed word's phonologicalor lexical ambiguity: Ambiguity effects stillremained in the delayed presentation. Thisoutcome probably suggests that auditory lexicalaccess was not completed within the 200 ms timeperiod.

We now turn to the effects of auditorydegradation. Superimposing noise on the auditorychannel affected subjects' performance, but itseffect was additive to the effects of phonologicaland lexical ambiguity, the spoken word'sfrequency, and the onset of print presentation.This outcome suggests that processing of themasked spoken words was independent of theprinted information. Apparently, the built-up ofphonological information necessary for theperception of the spoken word proceeded withoutreference to information derived from the printedform.

Recently, Frost and Katz (1989) proposed amodel that describes the mental lexicon ascontaining two levels of interactive relationshipbetween orthographic and phonologicalrepresentations: One level contains therepresentations of letters and phonemes andrelations between them. The other level involveswhole printed and spoken words. The relationsbetween spelling and sound in differentorthographies (Serbo-Croatian as opposed toEnglish, for example) was described in terms ofthe structural differences that exist among thevarious languages in respect to the relationshipbetween the orthographic and phonologicalsystems. In a similar way, phonological ambiguitycan be characterized by complex, non-isomorphicconnections between letters and phonemes, andlexical ambiguity can be characterized byambiguous connections between the orthographicand the phonological systems at the level of wholewords. The results of the present study provideadditional information as to how the phonologicaland orthographic systems interact in a shalloworthography like Serbo-Croatian.

The additive effect of auditory degradation andprint ambiguity suggests that the perception ofspoken words was not penetrated by informationfrom the orthographic system. When subjectsheard degraded speech, the presence of potentially

Phonological Ambiguity and Lexical Ambiguity: Effects on Visual and Auditory Word Recognition 99

helpful (i.e. phonologically unambiguous) print didnot, in fact, facilitate the match. Note, that sinceauditorily degraded and undegraded stimuli wererandomly mixed, subjects could not have adoptedone uniform strategy throughout the experimentalsession (e.g., favoring visual analysis when allstimuli were auditorily degraded). There are twopossible explanations for the absence of such aninteraction. Perhaps, our previous suggestion thatthe orthographic and phonological systems ex­change information at the level of singlegraphemes and phonemes (Frost & Katz, 1989;Frost et aI., 1988) should be constrained to deeporthographies-in which such an exchange mightbe beneficial. English could benefit from suchinteraction because in English some letters mayrepresent more than one phoneme. Accordingly,the exchange of information between the visualand the auditory modalities at this level canprovide the reader of English with additionalinformation for resolving ambiguity. In contrast,in Serbo-Croatian, the simplicity of the relationbetween letter and phoneme may preclude anyfurther improvement due to an interaction ofprinted and auditory information.

A second possibility for the absence of aninteraction between phonological ambiguity anddegradation is that the perception of spoken wordsmay be isolated from information derived fromorthographic processing. (This may not be amutual isolation; printed word perception may beinformed by the subword level by the presence of aspoken word.) The idea of an independent spokenwords processor is consistent with the charac­terization of speech perception as modular, in thesense of Fodor (1983). It is also consistent withrecent data from our laboratory suggesting thatthe simple detection of the presence or absence ofspeech in noise is not aided by the concurrentpresence of a printed word that corresponds to thespoken word that is embedded in the noise (Frostet al. 1988).

Finally, we suggest that examining the effects ofphonological and lexical amb~guity in Serbo­Croatian might provide insights into thedifficulties faced by the reader of English.Although there are relatively few words inEnglish that are phonologically bivalent for theskilled reader, there are many more that arephonologically ambiguous for the less skilledreader. The beginning reader of English oftencomes upon words that are, for himlher, of uncer­tain pronunciation. The reader may, therefore,decode a string into more than one possible

phonological realization that maps onto more thanone word in hislher lexicon. The ambiguity maysometimes be resolved by using contextual (i.e.,semantic) information but if the phonologicalinformation available to the reader is veryreduced, even contextual information may not beenough. In either case, the process of lexicalaccess for the less-skilled reader may be similar tothe process followed by the skilled reader for

. phonologically bivalent words. Thus, the phonolog­ically bivalent materials provides the researcherwith a way to model natural reading for theunskilled reader by means of the skilled reader. Oneadvantage of the present paradigm is thatphonological bivalence for the skilled reader can beintroduced and controlled experimentally.

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FOOTNOTES·Journal of Experimental Psychology: Learning, Memory, andCognition, 16,569-580. (1990).

tNow at the Department of Psychology, The HebrewUniversity, Jerusalem, Israel.

ttAlso State University of New York at Albany.tttAlso University of Connecticut, Storrs.

lIn genetal, effects of ambiguity tend to be greater for wordsthan for pseudowords.