Processing differences between nouns, adjectives, and verbs

Psychol Res (1987) 49:229-236 Psychological Research © Springer-Verlag 1987

Processing differences between nouns, adjectives, and verbs*

Aleksandar Kosti~ 1 and Leonard Katz 2

i Laboratory of Experimental Psychology, Faculty of Philosophy, Cika Ljubina 18-20, Y-11000 Belgrade, Yugoslavia 2 Haskins Laboratories and the University of Connecticut, 270 Crown St., New Haven, CT 06511, USA

Summary. Processing differences were investigated for nouns, adjectives, and verbs in Serbocroatian, a language that depends strongly on inflection to convey grammatical information. Four lexical decision experiments were run. Two of them inspected processing of inflected forms of nouns, demonstrating analogous processing for both singular and plural forms. Processing of the nominative case was faster for both grammatical numbers. Reaction times for the various case forms were not related to their respective frequencies of occurrence. Adjectival processing, on the other hand, gave no privileged role to the nominative case and the inflected form frequency had a strong influ- ence. Similarly, verbs also showed frequency-based processing. An explanation was proposed, suggesting that the organization of inflectional processing is dependent on the number of inflectional alternatives available to a given word.

The question addressed in this study concerns differences in the cognitive processing of grammatical inflection for different word types. The language of study is Serbocroa- tian, which depends strongly on inflection as its main grammatical device. For example, the case, number, and gender of each noun and each adjective in Serbocroatian is marked by means of a suffix added to the word stem. Nouns and adjectives appear in seven cases in both singular and plural, and there are three genders (masculine, feminine, and neuter) (see Appendies A and B). Likewise, verbs are marked for person, number, and tense (and sometimes for gender).

How does the native speaker/listener process an inflected word so that he or she understands not only the se- mantic message delivered by the stem, but also the syntactic message carried by the inflection? Consider the major syntactic descriptors of nouns and adjectives: case, number, and gender. The speed with which a listener or reader can perceive the whole word, that is, the base form and inflection (as measured, for example, in a lexical decision task) is, in part, a function of how rapidly the inflection can be processed (cf., Katz, Boyce, Goldstein & Lukatela,

* This research was supported by National Institute of Health (USA) grants HD-08495 to the University of Belgrade and HD- 01994 to the Haskins Laboratories.

Offprint requests to: A. Kosti6

1987). When comparisons are made among different inflected case forms of the same noun stem, differences in reaction time can not be ascribed to differences in the meaning of the base, which is identical for all the cases. Differences in responding to the various case forms must be due solely to the inflectional (case) differences among them. Such processing differences have been shown by Lu- katela and his associates in a number of lexical decision studies where nouns were presented in three singular cases (Lukatela, Mandi6, Gligorijevi6, Kosti6, Savi6, & Turvey, 1978; Lukatela, Gligorijevi6, Kosti6, & Turvey, 1980). In these studies it was demonstrated that recognition was fas- test for the nouns presented in the nominative case, which can be considered the citation form of the noun, that is, the form found in any standard dictionary. All the other case forms of the same nouns (the so-called "oblique cases") were recognized more slowly and had nearly equivalent latencies, even though they differed in the frequency of occurrence by as much as an order of magni- tude (Lukatela et al., 1980). This result indicated that the cognitive structural support for processing a noun inflection can be described, at least in part, as syntactic, since there are no other relevant characteristics that indicate the nominative-oblique distinction. Thus the nominative-oblique distinction is purely conceptual (cf., Lukatela et al., 1980, Katz et al., 1987).

As mentioned above, Serbocroatian adjectives, like nouns, also appear in seven cases and in both singular and plural. Adjectival inflection specifies case, number, and gender, and in that respect the adjectival system could be conceived of as being analogous to the noun system, with the nominative singular as the citation form. The citation form for verbs is the infinitive.

The present experiments were designed to determine whether the type of organization observed With singular nouns, that is, the privileged status of the citation form and absence of frequency effects, could be extended to their plural forms as well and to the other open class word types. To this end, we extended the investigation of inflectional processing differences to plural Serbocroatian nouns and to adjectives and verbs.

Experiment 1

Strong evidence exists for at least one cognitive syntactic processing effect: The inflectional processing system of Serbocroatian speakers distinguishes between nominative

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and oblique cases. The experiments of Lukatela and his associates have shown that the effect cannot be explained on the basis of phonological marking and is not grounded in the frequency of occurrence of the respective cases (Luka- tela et al., 1978, Lukatela et al., 1980, Katz et al., 1987). To confirm the assumption that the oblique singular cases are not organized by frequency and that the privileged role of the nominative case is not due to its relatively high frequency, Lukatela et al. (1980) contrasted the nominative singular with two oblique cases: one of approximately the same frequency as the nominative and one of lower frequency. The primacy of the nominative singular was re- tained, and again, no differences among the oblique cases w e r e found (Lukatela et al., 1980). On the basis of this evidence, Lukatela et al. (1980) suggested a cognitive model of the Serbocroatian noun system in which the nominative singular form assumed a central position; the oblique cases were considered to be uniformly clustered around the nominative singular. However, in these studies only cases in the singular form had been investigated and the proposed model makes no provision for plural forms. The model of Lukatela et al. (1980) allows for at least two plausible organizational patterns for the oblique plural cases. On the one hand, it could be assumed that the nominative plural and other plural forms are just additional oblique cases that, like the singular oblique forms, are uniformly clustered around nominative singular. According to this assumption, there should be no privileged processing for the nominative plural with respect to the oblique plural forms. An alternative assumption would produce an organization of the plural cases that is analogous to that of the singular forms, that is, no frequency-based organization to the cases and primary of the nominative plural with respect to the other plural forms.

A contrast between the two alternatives can provide clarification of the status of citation form. Although it is clear that the nominative singular form is privileged in some way during the process of word identification, it is less clear how to characterize this privilege more accurately. The question could be posed whether the processing advantage was due to the fact that the privileged form was (a) a nominative case form, per se, or (b) a citation form, that is, a nominative singular form, only. The question seeks to determine the important structural syntactic characteristic of the word identification process: Is the processing system most sensitive to nominative case forms, both singular and plural (and, by implication, most sensitive to the syntactic meaning of that case: subject-agent-topic) or is it most sensitive to the citation form, the nominative singular alone? I f the first alternative were true it would imply an analogous organization for singular and plural forms, that is, primacy of nominative plural with respect to other plural oblique forms. On the other hand, a sensitivity to citation form would predict no primacy for the nominative plural and a uniform organization of all cases, singular and plural, except for the nominative singular.

Directly contrasting the singular and plural is proble- matic, however. The nature of Serbocroatian morphology does not permit a contrast of all the inflected cases across the two grammatical numbers, because there are only three cases for masculine nouns that are unambiguously marked as plural (nominative, accusative, and instrumental), and only two of these (nominative and instrumental) also have a morphologically unique singular counterpart (see Ap-

pendix A). Therefore, it was not possible to use a factorial design. This means we cannot address a more general question about grammatical number and constrains our at- tention to the role of citation form in the plural and organization of plural oblique forms.

In the present experiment, three cases that are morphologically unique for singular (nominative, dative-locative, and instrumental) as well as the three cases morphologically unique for plural (nominative, accusative, and instrumental) were presented. Singular cases were presented in order to replicate the experiments of Lukatela et al.

M e t h o d

Subjects. Sixty-six first-year undergraduate students from the Department of Psychology, University of Belgrade, participated in the experiment as part of their academic requirements.

Materials and procedure. Seventy-two masculine nouns and seventy-two pseudonouns were selected. Each noun and pseudonoun was presented in three singular cases (nominative, dative-locative, and instrumental) and three plural cases (nominative, accusative, and instrumental). Nouns were equalized for length (five letters in the nominative form) and were from the medium range for frequency (Dj. Kosti6, 1965 a). Pseudonouns were created by altering one syllable in the middle of a real noun, thus preserving the characteristic phonological structure of Serbocroa- tian as well as correct case inflections. Stimuli were presented on a computer screen (Apple IIe). The subject's task was to answer as quickly and as accurately as possible by pressing the "yes" or "no" key, depending on whether the present string of letters was a word or not.

Design. Each subject saw a total of 144 stimuli (72 nouns and 72 pseudonouns). They were presented in such a way that subjects never saw the same stem twice but they saw all stems once, as well as all six cases. Nouns were divided into six groups of 12 nouns each. The 66 subjects were divided into six groups, each group containing 11 subjects. Subject in Group 1 saw the nominative singular of Catego- ry A nouns, dative-locative singular of Category B, and instrumental singular of Category C, nominative plural of Category D, and so forth. Subjects in Group 2 saw the nominative singular of Category B nouns, dative-locative singular of Category C, instrumental singular of Category D nouns, and so on. Subjects in Group 3 saw the nominative singular of Category C nouns, and so forth. The same partitioning into categories was done for pseudonouns as well.

Results and discussion. Reaction times less than 400 ms and longer than 1200 ms were excluded as well as latencies associated with erroneous responses. Table 1 presents the mean reaction times for responses to word trials for each of the six cases. The percentage of excluded items ranged from 2% to 5%.

Inspection of Table 1 suggests that the nominative case form of a noun was recognized faster than either of the two oblique case forms and that this pattern was essential- ly the same for singular and plural. Two separate analyses of variance, one for each grammatical number, were performed on both subject and item data. Analysis of the

Table 1. Mean latencies (in ms) for nouns in experiment 1

Case RT ~

Nominative singular 679 Dative/locative singular 744 Instrumental singular 744 Nominative plural 716 Accusative plural 768 Instrumental plural 758

~, RT = reaction time

three singular cases showed a significant effect of case for both subject and item analyses, F(2,130)=63.74, MSe=1415, P<0.01 for subjects, and F(2,142)=24.7, MSe= 4087, P< 0.01 for items. A contrast between the two oblique singular cases was not significant, while significant differences were found between the nominative and dative-locative and also between nominative and instrumental; both differences were significant at P<0.01 for both subject and item analyses. These results confirm the previous findings of Lukatela et al. (1978, 1980) of nominative case superiority. A separate analysis, performed on plural cases only, showed a significant main effect of case for both subject and item analysis, F(2,130)=30.61, MSe= 1530, P<0.01 for subjects, and F(2,142)= 15.44, MSe= 3554, P< 0.01 for items. No difference between the two oblique cases was found, but a contrast between nominative and accusative case was significant, as was a contrast between nominative and instrumental cases, both at P< 0.01 for both subject and item analyses.

The main evidence upon which Lukatela et al. (1978) built their argument that inflected cases are not organized by frequency was the fact that no difference was found between the two oblique cases, although they differed in their respective frequencies. The same kind of argument can be applied here as well. The absence of difference in word recognition time between the two oblique plural forms, in spite of their respective differences in frequency (see Ap- pendix D) suggests that plural forms are not organized by frequency.

The results suggest that plural nouns may be organized in the same fashion as the singular ones. No indication of a frequency-based organization for the plural noun forms was found. In addition, the nominative plural appears to be the privileged case among plural forms. Thus, it appears that we can reject the likelihood that the processing mechanism is sensitive to the citation form qua citation form. Although these data are highly suggestive, they need further confirmation. In particular, the superiority of the nominative plural should be more stringently tested for the following reason: Although its latency was the shortest among plural cases, it also had a higher frequency than the two oblique plural forms. Even though we can apparently reject a frequency explanation of its superiority, prudence dictates that a more direct attack on the frequency hypo- thesis is desirable.

Experiment 2

In order to confirm the suggestion that the nominative plural indeed has a privileged status, a more severe test was applied; namely, one which contrasts nominative plural with an oblique case that either does not differ in frequen-

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cy or has a greater frequency than the nominative. If the nominative plural still has a faster identification time, then the difference cannot be ascribed to frequency. The most promising candidate for such a comparison is the genitive case. The genitive singular and plural forms of masculine nouns are identical in form; together they have a compound frequency which is substantially larger than that of nominative plural (see Appendix D). If the relative position of the nominative plural's identification latency is not frequency-determined, its processing time should be faster than, or at least equal to, the genitive singular although they differ drastically in frequency. On the other hand, if genitive singular appears to have a shorter latency, no firm conclusion can be made either about the role of frequency in the overall organization of the noun system or about the assumed privileged position of the nominative form. The present experiment parallels Experiment 1 in all respects except one: nominative singular is substituted for genitive singular/plural. The two oblique plural cases were presented.in order to confirm the indication obtained in the first experiment about the privileged role of nominative plural with respect to the other oblique plural forms.

Subjects and procedure. Seventy first-year undergraduates from the Department of Psychology, University of Bel- grade, participated in the experiment as part of their academic requirements. Stimuli, design, and procedure paralleled those in Experiment 1.

Results and discussion. Three separate analyses of variance, one for each grammatical number, were performed. Reaction times less than 400 ms and longer than 1200 ms were excluded, as were latencies associated with erroneous responses. The rate of the excluded items was similar to that in the first experiment. Mean latencies are presented in Table 2.

No main effect of case was obtained for the three singular forms. However, there was a significant effect of case for the plural forms, F(2,130)=54.7, MSe= 1445, P<0.01 for subjects, and F(2,142)=22.9, MSe=3591, P<0.01 for items. As before, contrast between the two oblique plural cases was not significant and primacy of the nominative plural was replicated; significant differences were obtained between nominative plural and accusative plural as well as between nominative plural and instrumental plural, P<0.01. The crucial contrast, however, was between the compound genitive form and the nominative plural. Inspection of Table 2 suggests little difference between nominative plural and the genitive. This difference was marginally significant for the subject but not the item analysis: t(70)= 6.33, P< 0.05. Moreover, the questionable difference is in the opposite direction than would be predic-

Table 2. Mean latencies (in ms) for nouns in experiment 2

Case RT

Genitive singular 612 Dative/locative singular 602 Instrumental singular 614 Nominative plural 599 Accusative plural 652 Instrumental plural 662

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ted by frequency: the less frequent nominative plural has a shorter latency than the compound genitive. This finding indicates that processing of the nominative plural with respect to other plural forms is not determined by its frequency of occurrence.

In sum, Experiments 1 and 2 suggest analogous processing for both the singular and plural forms of a noun. The privileged status of the nominative form is confirmed for the plural as well as for the singular. These findings cannot be explained on the basis of the frequencies of occurrence of the forms. Finally, there is a suggestion that grammatical number may be an additional syntactic factor that influences processing, although no firm conclusion could be made since no comprehensive singular-plural contrast is available.

Experiment 3

Because Serbocroatian adjectives have inflectional suffixes that indicate case, gender, and number, we might expect them to act like nouns with regard to an ordering of word recognition times to the various case forms. Thus, we might expect them to divide into two sets: nominative and oblique. On further consideration, however, one can see a formal syntactic difference between adjectives and nouns that complicates any attempt to assign the same processing mechanisms to both; there is an important difference between the two with respect to their syntactic roles. Namely, in grammatical agreement the adjective is morphologically modified by the noun. That is to say, the adjective has to assume the morphological arguments of its noun complement, including case, number, and gender. As a conse- quence, gender is not an intrinsic characteristic of an adjective, as it is of a noun (see Appendix B). Instead, an adjective must take on the gender of the complementing noun. For example, the noun polje ("field") is known by a native speaker to have the neuter gender; all of its inflections will be produced and understood within this constraint. In contrast, the adjective ~iroki/a/o/("wide") has no intrinsic gender but instead adopts the gender of the noun (e.g., ~iroko polje/"wide field"). However, when in a phrase with a feminine noun, for example, staza ("road"), the adjective takes on the inflection appropriate for a fe- mine noun (giroka staza/"wide road"). By virtue of being modified by a noun and thus having no intrinsic gender, Serobocroatian adjectives can appear in 42 different grammatical forms: seven cases, two numbers, and three genders.

The major question addressed in this experiment is whether processing of an inflected adjective parallels that of a noun or whether its different syntactic role is reflected in a different principle of processing. In other words, will adjectives exibit processing that is not frequency based and that, in addition, displays superiority for nominative singular and plural forms?

Subjects. Sixty-six first-year undergraduates from the De- partment of Psychology, University of Belgrade, participated in the experiment as part of their academic requirements.

Materials. Seventy-two adjectives of masculine gender, equalized for frequency and length (Kosti6, 1965a) and seventy-two pseudoadjectives were presented in the exper-

iment. The constraint encountered in the first two experiments was present in this experiment as well. Namely, due to the morphological characteristics of Serbocroatian adjectives, it was not possible to find several singular cases within a defined gender that have morphologically unique counterparts in the plural. Therefore, three uniquely singular and three uniquely plural forms in masculine gender were selected, out of which two were analogous across grammatical number (nominative and genitive). In addition, dative-locative singular and accusative plural were presented.

Pseudoadjectives were formed by altering one letter in the middle of a real adjectival stem, thus preserving an appropriate phonological structure as well as the case inflections. Both adjectives and pseudoadjectives were presented in six case forms. The cases chosen were morphologically distinct and, therefore, they unequivocally speci- fied only one case and, with one exception, one number as well (see Appendix B). The exception derives from the fact that for adjectives, unlike nouns, the nominative plural can coincide morphologically with the definite form of the nominative singular. For example, the adjective visoki ("tall") is both the nominative singular definitive form ("the tall one") and the indefinite nominative plural ("tall ones"). In contrast, the indefinite form of the nominative singular is inflectionally unique, namely, visok. I f both singular and plural nominatives assumed a privileged role in adjectival processing, the distinction between the two would parallel the one observed with nouns. On the other hand, if frequency dominates adjectival processing, the nominative plural, confounded with the nominative singular definitive form, should be recognized faster, since its frequency exceeds that of the unique nominative singular.

Design and procedure. The 72 adjectives and 72 pseudoadjectives in three cases, singular and plural, were presented in such a way that each subject saw all adjective and pseu- doadjective stems as well as all inflected cases (both singular and plural) but never saw the same stem twice. This was obtained through a design which paralleled that of Ex- periment 1 and 2. The task, lexical decision, and the medium of presentation (computer-controlled video screen) were the same as in Experiment 1.

Results and discussion. Reaction times shorter than 400 ms and longer than 1200 ms were excluded, as were the erroneous responses. The rate of the excluded items ranged from 2% to 4%. Mean latencies are presented in Table 3.

Analyses of variance on mean reaction times for subjects, performed separately for singular and plural cases, revealed significant differences among the three cases within each number, F(2,130)=3.78, MSe= 1372, P< 0.03

Table 3. Mean latencies (in ms) for adjectives in experiment 3

Case RT

Nominative singular 752 Genitive singular 744 Locative singular 765 Nominative plural 725 Genitive plural 756 Accusative plural 747

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for singular forms and F(2,130)= 13.86, M S e = 1175, P<0.01 for plural forms. For item analysis, a significant effect of case was found for the plural forms; F(2,142)=4.92, M S e = 3 2 3 4 , P<0.02, but not for the singular ones.

Inspection of Table 3 suggests no primacy of the nominative singular form. The difference between nominative singular and genitive singular was not significant. Further, the contrast between nominative singular and dative-locative singular proved to be significant on subjects but not on items. However, the difference between the two oblique cases themselves was significant, P< 0.01, apparently due to their respective frequencies. These findings, that is, no primacy of nominative singular and a difference between the oblique cases, suggest a strong departure from the organization of the inflected cases observed within a noun system. For the plural adjectives, a significant difference was obtained between nominative plural and genitive plural, as well as between nominative plural and accusative plural, but no difference was found between the two oblique plural forms. In contrast to the singular forms, this pattern does not seem to differ from the one obtained with nouns. On closer inspection of the frequencies of occurrence, however (see Appendix E), those differences in latencies seem to coincide with frequencies of occurrence including both singular and plural forms. For nouns, we were able to further test (and to reject) the frequency hy- pothesis by comparing the nominative plural with the compound genitive: The former was less frequent than the latter but, nevertheless, it had a shorter latency. For adjectives, no such comparable situation exists; the nominative plural is, in fact, more frequent than either the genitive singular or the genitive plural (they are not identical forms). Thus, in support of a frequency explanation for adjectives, we must rely on (1) the absence of a nominative superiority for the singular and (2) for both singular and plural, a strong correlation between frequency and latency. Even so, there is ample reason to doubt that nominative superiority exists for adjectives. It seems implausible that a true processing advantage could exist for the nominative plural but not for the nominative singular; the singular form is at least coincident with the citation form, while the plural form is used only for its case meaning, a use it shares with the singular.

In order to consider the effect of frequency more precisely we must first distinguish between two ways of deter- mining case frequency. By virtue of having three genders, adjectives, as already noted, appear in 42 different grammatical forms, only 14 of which are morphologically distinct. This implies that some forms are identical across different genders and numbers. Therefore, there are two possible frequency counts: one that includes compounding of the frequency of a suffix only within a single gender (in this case masculine) and another that would include compounding of the frequencies of morphologically identical forms across gender and number. This contrast may, in turn, illuminate some uncertainties about the strategy a subject uses while processing inflected adjectives. The question is whether adjectival processing, being affected by frequency, is constrained by the frequency within the particular gender of the stimulus or whether it is influenced by the frequency of a particular morphological form, no matter what its syntactic attributes may be. In- spection of the two log-frequency patterns, contrasted with

the mean latencies for adjectives, suggests that there is a closer conformation to latency for the log frequencies compounded across gender and number. This suggests that adjectival processing may be affected by the compound frequency of a particular morphological form (i. e., the frequency with which that physical form appears, without respect to the syntactic meaning) rather than by the frequency of that form conditional on gender. In order to test this suggestion, linear correlations between mean latency and the two log frequency indices were calculated. A signifi- cantly higher correlation coefficient between latency and the log of the compound log frequency suggested that processing of adjectival inflection is influenced by the compounded frequency of a particular morphological form (compounded across number and gender). However, in the absence of more reliable statistics, this finding is only suggestive rather than conclusive.

The lack of superiority of nominative singular and the likelihood that adjectival inflected forms are influenced by their respective frequencies of occurrence indicate a principle of processing that differs sharply from the one observed with nouns. While both word types were probed across the same syntactic parameters (i.e., case and number), adjectives, in contrast to nouns, appear to be affected by the respective case frequencies, with no privileged status accorded to the nominative forms.

What might be the reason for the observed processing differences between adjectives and nouns? Or, to put it differently, what are the differences between the two word types that may cause distinct processing outcomes? There seem to be two major distinctions: One refers to their different syntactic roles, while the other resides in the difference of the number of grammatical instances each word type can assume (14 for nouns vs 42 for adjectives). Dis- tinct syntactic roles may account for the differences in the way that the cases are recognized. Case roles are, perhaps, naturally determined first for a noun (whether in listening/reading or speaking/writing) and merely copied to the adjective member of the pair. That is, case roles may involve a kind of primary process for nouns but only sec- ondary one for adjectives. I f so, this implies that the observed difference between nouns and adjectives is a function of the adjective's dependency on the noun, thus being idiosyncratic to the respective word type. On the other hand, if the processing differences are due to the number of grammatical instances, adjectives should share their principle of processing with another word type, which is also characterized by a large number of grammatical instances. The latter alternative is probed in the next experiment.

Experiment 4

In order to determine which of the two kinds of explanations accounts for the differences between noun and adjective processing, we studied a third word type that is (a) unlike either adjectives or nouns in that it neither extensively modifies nor is modified by any other open-class word type but nevertheless has (b) at least as many inflections as the adjectival system. Verbs are a candidate for such a comparison. As already mentioned, the Serbocroatian verb has three persons in both singular and plural; all are uniquely marked morphologically. Verbs are also marked for tense, and sometimes for gender. The verb phrase "I

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sing", for example, is formed by adding the suffix m (which specifies first person singular, present tense) to a base form peva-, giving pevam; "You sing" is pevag, and so forth (see Appendix C). A large number of verb forms exists; when all grammatical attributes are taken into consideration, each Serbocroatian verb can appear in 314 different inflectional forms, of which 211 have a measured occurrence of 1 per 3 million or greater in the Kosti6 (1965b) norms. Thus, the number of distinct grammatical instances of Serbocroatian verbs far exceeds that of adjectives. In addition, in Serbocroatian a verb can stand alone as a grammatical utterance (e. g., pevam, "I sing"). A noun or pronoun is never an obligatory complement to the verb. Thus, verbs appear to be a proper word type for the contrast we seek since (a) they are characterized by a large number of formal grammatical instances but (b) unlike adjectives, they are not consistently modified by or used to modify nouns.

In the present experiment, verbs were presented in three persons singular and plural, and in present tense. There were two possible outcomes to the experiment. One potential outcome was a pattern of response latencies that was not a function of inflectional frequency, thus paral- leling the result encountered with nouns. With such an outcome, it could be argued that none of the explanations of- fered for nouns and adjectives (i. e., syntactic role and/or number of inflectional alternatives) can account for the organization of words with inflected morphology, because nouns, which showed just such a result, share neither role nor number of inflections with verbs. The alternative outcome, namely the finding that verb tatencies were a function of inflectional frequency, would suggest the opposite: that frequency-related processing is (a) not something idiosyncratic to adjectives and their particular syntactic role and, therefore, (b) likely to be related to the number of inflectional alternatives.

Subjects. Sixty-six first-year undergraduates from the De- partment of Psychology, University of Belgrade, participated in the experiment as part of their academic requirements.

Materials. Seventy-two verbs and seventy-two pseudoverbs were selected in the first, second, and third persons singular and plural, present tense. The verbs selected were equal in frequency and length; all were five letters long in the first person singular. Pseudoverbs were created from real verbs by altering one letter in the middle of the stem.

Design and procedure. The procedure in the present experiment paralleled that of the previous ones. Every subject saw all verbs and pseudoverbs as well as all inflectional forms (three persons, singular and plural). However, none of the stimuli was presented twice to the same subject. This was achieved through the design applied in Experiments 1, 2, and 3. As in the previous experiments, the subject's task was in the form of a lexical decision.

Results and discussion. Table 4 presents the mean reaction times to each of the combinations of person (first, second, and third) and number (singular, plural). Reaction times shorter than 400 ms and longer than 1200 ms were excluded. The rate of items excluded ranged from 3% to 5%.

Table 4. Mean latencies (in ms) for verbs in experiment 4

Person Singular Plural

First 700 715 Second 710 717 Third 687 709

Analyses of variance on subject and item means indicated that the main effect of person was significant for subjects, F(2,130) = 3.49, MSe= 2300, P< 0.04, but not for items. In contrast, the effect of number was significant for both subjects F(1,65)=8.66, MSe=2457, P<0.005, and items, F(1,71) = 4.68, MSe= 4971, P< 0.04. No significant person by number interaction was obtained, indicating that similar patterns were obtained for singular and plural forms. In a post hoc t-test, a significant difference between second and third person singular was obtained in subject and item analyses, P<0.01. It can be hypothesized that this difference derives from the difference in length between the two persons, since the second person singular has an additional letter. However, this does not seem prob- able, because significant differences (P<0.01) were obtained (for both subject and item analyses) in the third person between singular and plural, which are equivalent in length. Likewise, there was no difference between the second person singular and all three plural persons, in spite of the fact that the third person plural has one letter less and the first and second persons plural have one letter more than the second person singular. Inspection of Ap- pendix F indicates, however, that the latencies for the inflected verb forms apparently coincide with their frequencies of occurrence. In order to test this assumption a linear correlation was calculated (r=0.89, P<0.05) suggesting that verbs, like adjectives, might be organized by frequency as well.

General discussion

The outcomes of the present experiments suggest processing differences between nouns on one hand and adjectives and verbs on the other. Experiments 1 and 2 support the findings of Lukatela et al. (1978, 1980), and, in addition, demonstrate an analogous organization for the plural inflected cases as well. No effect of frequency was observed for the oblique plural forms, while the primacy of the nominative plural case paralleled that of the nominative singular. However, in contrast to nouns, adjectival processing does not show any privileged position for the nominative case. Nominative singular and plural do not have a pivotal role with respect to the oblique forms. Significant differences were found between some adjective oblique cases, indicating that the oblique cases do not parallel the uniform arrangement of the noun oblique forms. Instead, there is a suggestion that the adjectival oblique forms may be organized by their respective frequencies. In addition, it was demonstrated that latencies of inflected verbs are ar- ranged in a pattern that mirrors their frequency of occurrence.

What are the sources of these processing differences among word classes? To put the question more precisely, what structural linguistic differences exist among the three word classes that might cause the processing differences

we have observed? Three kinds of distinctions appear to be plausible candidates. The first distinction can be made with respect to the syntactic roles each word type can take; nouns, adjectives, and verbs assume different roles in a sentence. A second distinction is that of the grammat ica l / morphological attributes that characterize each word type. Finally, the third distinction is based on the number of alternative inflectional forms in which nouns, adjectives, and verbs can appear.

Consider the syntactic roles of adjectives, nouns, and verbs. Adjectives are determined by nouns in case, number, and gender; all grammatical attributes of an adjective are parasitic on the grammatical attributes of the noun. This, however, is not true for verbs. While a noun deter- mines a verb's person and number , it does not modify its tense and aspect. In other words, adjectives and verbs differ with respect to their inflectional independence from their noun complements. If these different relationships determined the way different word types were organized, one might expect to find different processing principles between adjectives and verbs. This, however, is not the case; in fact, adjectives and verbs are apparently recognized in similar ways. Their different syntactic roles do not lead to important differences in their sensitivity to inflec- t ional frequency.

The second distinction among the three word types derives from their grammatical /morphological properties. As already noted, adjectives and nouns share common morphological attributes (case, number , and gender). Verbs, on the other hand, are characterized by person, number , and tense. If grammatical /morphological properties were the factor that determined the overall organiza- t ion of different word types, one might expect adjectives and nouns to be organized by the same principle, in contrast to verbs. The results of the present experiments do not support such an assumption, because the grammatical /morphological commonalit ies do not result in processing similarities for nouns and adjectives.

The third criterion for differentiation among the three word types is the number of functionally different grammatical instances each type can have. As already mentioned, each Serbocroatian noun can appear in seven cases singular and seven cases plural. Nine out of these fourteen forms are morphologically unique. Adjectives, on the other hand, can assume more inflectional forms (42), only 14 of which are morphologically unique. It does not seem plausible that the number of morphologically distinct forms is the appropriate dist inction; according to this criterion, there is apparently only a small difference between adjectives and nouns on this variable. Finally, each Ser- bocroatian verb can appear in 314 grammatical roles ei-

Appendix D Percentage occurrences of different cases for nouns

Appendix A Declension of masculine nouns

Case Singular Plural

235

Nominative TALAS, TALASI Genitive TALASA TALASA Dative TALASU TALASIMA Accusative TALAS TALASE Vocative TALASE TALAS1 Instrumental TALASOM TALASIMA Locative TALASU TALAS1MA

~' TALAS = WAVE

Appendix B Declension of adjectives

Case Singular

Masculine Feminine Neuter

Nominative VISOK(I) a. b VISOKA VISOKO Genitive VISOKOG VISOKE VISOKOG Dative VISOKOM VISOKOJ VISOKOM Accusative VISOK(OG) VISOKU VISOKO Vocative VISOKI VISOKA VISOKO Instrumental VISOKIM VISOKOM VISOKIM Locative VISOKOM VISOKOJ VISOKOM

Case Plural

Masculine Feminine Neuter

Nominative VISOKI VISOKE VISOKA Genitive VISOKIH VISOKIH VISOKIH Dative VISOKIM VISOKIM VISOKIM Accusative VISOKE VISOKE VISOKA Vocative VISOKI VISOKE VISOKA Instrumental VISOKIM VISOKIM VISOKIM Locative VISOKIM VISOKIM VISOKIM

a VISOK = TALL b Suffixes in parentheses denote accusative singular for animate

nouns and definitive form for nominative singular

Appendix C Conjugation of verb in present tense


First RA D I M ~' RADI MO Second RADIS RADITE Third RAD1 RADE

RADIM = I WORK


Masculine Feminine Neuter Masculine Feminine Neuter

Nominative 12.94 8.84 2.88 3.33 3.58 0.69 Genitive 8.56 7.88 3.47 3.96 3.22 0.61 Dative 0.87 0.38 0.31 0.28 0.16 0.04 Accusative 5.49 5.48 2.55 2.21 2.75 0.73 Instrumental 1.90 1.94 0.86 0.60 0.80 0.13 Locative 3.77 3.42 1.61 0.61 0.80 0.21

This table is adapted from Dj. Kosti6 (1965 b). Percentages do not add up to 100% because the vocative case has been omitted

236

Appendix E Percentage occurrences of different cases for adjectives


Masculine Feminine Neuter Masculine Feminine Neuter

Nominative 12.94 10.73 3.91 4.62 4.89 1.18 Genitive 5.49 6.27 2.36 3.90 3.73 0.92 Dative 0.61 0.50 0.21 0.27 0.18 0.05 Accusative 5.09 4.98 2.12 2.48 3.27 1.02 Instrumental 1.64 1.57 0.66 0.68 0.79 0.20 Locative 2.22 2.29 0.99 0.88 0.85 0.24

This table is adapted from Dj. Kosti6 (1965 b). Percentages for comparative and superlative are not included

ther as an individual morpheme or as a morpheme which requires an auxil iary verb in order to specify a par t icular grammatical form. According to this cri terion, there is a major dist inction between the three word types. Namely , a given noun appears in a relat ively small number of inflec- t ional roles, while adjectives and verbs are word types with a large number of funct ional ly distinct forms. The effects of this dist inct ion in processing the inflected informat ion of the different word types needs addi t ional inspect iom

Appendix F Percentage occurrence of verb in different persons, in present tense


First 12.34 3.97 Second 3.97 1.33 Third 49.77 23.38

This table of percentages is adapted from Dj. Kosti6 (1965 b)

References

Katz, L., Boyce, S., Goldstein, L., & Lukatela G. (1987). Gram- matical information effects in auditory word processing. Cog- nition, 25, 235-263.

Kosti6, Dj. (1965a). Frequency dictionary of the Serbocroatian language. Belgrade: Institute of Experimental Phonetics and Speech Pathology.

Kosti6, Dj. (1965b). The structure of usage value of grammatical forms in the Serbocroatian language. Belgrade: Institute of Ex- perimental Phonetics and Speech Pathology.

Lukatela, G., Gligorijevi~, B., Kosti6, A., & Turvey, M. T. (1980). Representation of inflected nouns in the internal lexicon. Memory & Cognition 8, 415-423.

Lukatela, G., Mandi6, Z., Gligorijevi6, B., Kosti6, A., Savi6, M., & Turvey, M. T. (1978). Lexical decision for inflected nouns. Language and Speech 21,166-173.

Received October 20/November 21, 1986

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Processing differences between nouns, adjectives, and verbs