What Is a Word? Recognizing Polymorphemic Lexical Items in DLI

Brain and Language 68, 254–261 (1999) Article ID brln.1999.2110, available online at http://www.idealibrary.com on

What Is a Word? Recognizing Polymorphemic Lexical Items in DLI Phaedra Royle and Gonia Jarema Universite´ de Montre´al and Centre de recherche de l’institut universitaire de ge´riatrie de Montre´al, Montreal, Quebec, Canada

and Eva Kehayia McGill University and Research Department, Jewish Rehabilitation Hospital, Montreal, Quebec, Canada This paper addresses issues of frequency and transparency in word recognition and their importance for the organization of the mental lexicon in Developmentally Language Impaired (DLI) francophones. A simple visual lexical decision task probes responses of DLI and control participants when presented with verbs. DLI participants are sensitive to whole-word frequency and show little or no transparency effects. These results are interpreted as indicating that words are not organized according to ‘‘morphological families’’ in the DLI mental lexicon, but rather according to a principle of frequency. These facts support the hypothesis that words in the DLI mental lexicon lack lexical features and morphological structure.  1999 Academic Press

Key Words: developmental language impairment; mental lexicon; French; frequency; morphological transparency.

INTRODUCTION

Across languages, DLI subjects show difficulties in appropriately producing, judging, and correcting inflected verb forms (see Clahsen, 1989; Leonard, Bortolini, Carelli, McGregor, & Sabbadini, 1992; Kehayia, 1997; DalaThe authors thank the anonymous reviewers for their comments. The research in this paper was supported by an MCRI (Major Collaborative Research Initiative) grant from the Social Sciences and Humanities Research Council of Canada (Grant No. 412-95-0006) and an MRCSSHRC (Medical Research Council and Social Sciences and Humanities Research Council) Intercouncil Grant (SP-12754). The first author acknowledges a Ph.D. research scholarship from the Fonds pour la Formation de Chercheurs et l’Aide a` la Recherche (Ref. No. 983304). Address reprint requests to Phaedra Royle, Centre de recherche, Institut universitaire de ge´riatrie de Montre´al, 4565 chemin Queen-Mary, Montreal, Quebec H3W 1W5, Canada. 254 0093-934X/99 $30.00 Copyright  1999 by Academic Press All rights of reproduction in any form reserved.

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lakis; 1996, Gopnik, Dalalakis, Fukuda, Fukuda, & Kehayia, 1996). Similar results have been reported for French-speaking subjects (Rose & Royle, 1999). Research has demonstrated that frequency is a determining factor affecting both acquisition of lexical items (Rice, Oetting, Marquis, Bode, & Paye, 1994) and verb production (Rose & Royle, 1999; Royle, 1996; Ullman & Gopnik, 1994) in this population. Moreover, degree of morphological transparency (i.e., regularity of an inflectional paradigm) and word internal structure, which are instrumental in nonimpaired lexical access and representation, appear to be without consequence for DLI subjects (Kehayia, 1994, 1997). Based on these findings, it has been proposed that DLI subjects lexicalize verbs as ‘‘whole chunks’’ without any internal morphological structure (Kehayia, 1994, 1997). This implies that their morphological module is nonexistent or damaged. This study addresses the issue of access and representation of inflected items in the mental lexicon of French-speaking DLI subjects. It investigates the extent to which the presence of an overt morphological deficit reflects differential word recognition patterns and a structurally ‘‘altered’’ mental lexicon. A simple visual lexical decision task is used to probe whether frequency and morphological transparency play a role in verb recognition by DLI subjects. HYPOTHESES

Assuming that DLI subjects have a morphological deficit, we hypothesize that they will not be able to parse polymorphemic words during word recognition and that they list words as whole chunks. Consequently, factors such as frequency, but not morphological transparency, are anticipated to play a significant role during word recognition. METHOD

Materials Frequency and transparency factors were manipulated by grouping French verbs into four classes: FR (Frequent Regular) (e.g., prier/pɹIye/to pray) FI (Frequent Irregular) (e.g., mordre/mɔɹd(ɹ)/to bite) IR (Infrequent Regular) (e.g., friser/fɹIze/to curl) II (Infrequent Irregular) (e.g., teindre/tε˜ d(ɹ)/to dye) Irregularity was defined as a form with more than one stem in its inflectional paradigm. Compound frequency counts were based on Brulex (Content, Mousty, & Radeau, 1990).

Participants Ten pairs of participants, all native speakers of Quebec French, from families with histories of DLI (drawn from the McGill University Genetic Dysphasia Project, M. Gopnik, Director)

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TABLE 1 Average CRs by Type of Verb (% correct) Frequent regular DLI Control

Average 81.8 95.3

Frequent irregular

SD 17.1 7.8

Average 83.6 95.8

SD 15.3 7.1

Infrequent regular Average 78.9 93.6

SD 18.7 9.8

Infrequent irregular Average 59.3 77.3

SD 20.4 16.6

and controls matched for language and age (14/7 to 50/3 years of age) participated in the simple lexical decision task (SLD).

Design and Procedure All participants were tested using the PsyScope 1.01 application for Macintosh (Cohen, MacWhinney, Flatt, & Provost, 1993). The following sequence was presented: a 500-ms pause; a mask (#####) lasting 250 ms; a 250-ms pause and the stimulus, which stayed on the screen until a response was given. Both mask and stimulus were presented in the center of the computer screen. Participants were asked to press the ‘‘yes’’ key if they recognized the item as a French word and the ‘‘no’’ key if they did not. The SLD task was run in a single test of six blocks containing 528 trials. The experiment had 180 experimental stimuli, 120 fillers (nouns and adjectives) and 228 nonwords constructed by changing the first consonant of the fillers and stimuli. All runs were randomized. Latency (RT) and response accuracy (CR) were the dependent variables. Three independent variables were used: verb frequency (F, I), verb type (R, I) and inflected form—infinitive (infinitive), 2ps present (2s), 2pp present/imperative (2p),1 3ps imperfect past (imperfect), and 3ps present (3s). Stimuli that had shown poor responses (over 30% error) by a control group of 30 participants were eliminated from the analysis.

RESULTS AND DISCUSSION

Correct Responses DLIs showed lower CR rates than controls: DLI 75.9% (SD 20.3); control 90.5% (SD 13.3), (F(1, 18) ⫽ 13.96, p ⬍ . 01). Significant main effects of verb form (F(1, 18) ⫽ 7.8, p ⬍ . 01), frequency (F(1, 18) ⫽ 43.33, p ⬍ .01) and transparency (F(1, 18) ⫽ 28.30, p ⬍ . 01) were found. Verb form distinguished both groups of subjects (F(1, 18) ⫽ 3.5, p ⫽ .01). Analyzed separately, both groups of participants showed main effects of frequency (F DLI (1, 9) ⫽ 22.33, p ⬍ . 01; F C (1, 9) ⫽ 21.76, p ⬍ . 01) and transparency (F DLI (1, 9) ⫽ 9.79, p ⬍ .01; F C (1, 9) ⫽ 32.97, p ⬍ . 01) and an interaction effect for frequency and transparency on CRs (F DLI (1, 9) ⫽ 11.62, p ⬍ . 01; FC (1, 9) ⫽ 18.48, p ⬍ . 01). This interaction is plotted in Table 1. The patterns for both groups seem to be parallel. However, a different tendency for each of the groups emerges from a comparison of the RT data. 1 The 2pp present and the 2pp imperative are homophonous homographs (e.g., mangez/ ma˜Ze/‘you-pl.-eat’ and ‘eat (!)’).

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FIG. 1. Interaction of transparency and frequency on reaction times: lozenges are DLI participants, squares are controls.

A main effect of form was found for controls, (F C (4, 0) ⫽ 3.32, p ⫽ .02) and no main effect of frequency or transparency. However, an interaction effect of frequency and transparency was found for RTs in this group (F C (1, 0) ⫽ 20.68, p ⬍ . 01). This interaction is illustrated in Fig. 1. DLIs showed a main effect of frequency (F(1, 0) ⫽ 10.35, p ⫽ .01) and of form (F(4, 0) ⫽ 3.94, p ⫽ .01), but no interaction of transparency and frequency (F(1, 0) ⫽ .24, p ⫽ ns). All frequent verbs were accessed faster than infrequent verbs, regardless of transparency. This contrasts strongly with the controls’ patterns. Controls seemed to recognize all regular verbs at the same speed whether they were frequent or not. This was not the case with irregular verbs. The results confirm the roles of transparency and frequency in lexical decision tasks for unimpaired subjects. Therefore, although DLI participants showed parallel (albeit lower) CRs, this does not mean that they are processing words in the same manner as controls. The RT data shows that there are qualitative differences in word recognition patterns for both groups. Transparency was predicted not to play a significant role in the recognition of words by DLI participants. This hypothesis is borne out only by the RT data. It is plausible that recognition of a word can also be affected by the regularity of a paradigm, although morphological processes are not involved in the recognition process. It has been proposed that DLI subjects use analogy to create inflected-like forms (Paradis & Gopnik, 1994) to account for their ability to produce a number of correct responses during linguistic tasks. If analogy is used to recognize words, then a verb that follows a regular pattern might result in higher levels of CR by virtue of its possible use in a paradigm. An irregular verb would be more difficult to integrate.

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TABLE 2 Average CRs by Verb Form (% Correct) Infinitive

DLI Control

3s

2s

Imperfect

2p

Average

SD

Average

SD

Average

SD

Average

SD

Average

SD

84.5 93.6

16.7 10.6

76.8 90.8

15.9 11.4

70.9 84.9

21.9 14.6

78.1 90.1

18.9 16

69.3 93.1

24.2 12.1

As outlined above, the verb form variable shows a main effect on correct recognition patterns, and also differentiates between the two groups, as illustrated in Table 2. This main effect is due to high error rates seen on DLIs’ recognition of the imperfect form (F(1, 9) ⫽ 8.06, p ⬍ .01) and is probably related to the low type frequency of the -ait inflection of the imperfect form in colloquial French. By comparing the two groups of subjects on the infinitive (high token frequencies) and imperfect (low token frequencies) forms, one finds again a significant effect of form for DLIs (F(1, 9) ⫽ 15.39, p ⬍ .01) but no effect of form for controls (F(1, 9) ⫽ .13, p ⫽ ns). This is illustrated in Fig. 2. Thus, token frequency has a strong effect on whether a form will be correctly recognized by DLI participants. More frequent verbs are recognized at a higher rate of accuracy. However, even if a given item is part of a verb paradigm with high compound frequency, its correct recognition by a DLI subject will be impeded if it is of low token frequency. Controls showed a different pattern. The compound frequency of the verb, and not the token frequency, influenced their recognition patterns for verbs.

FIG. 2. Form and frequency effects on correct responses: imperfect versus infinitive verb forms that are both frequent and infrequent.

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TABLE 3 Average RTs on Verb Forms (ms) DLI

Control

Form

RT

SD

RT

SD

Infinitive 3s 2s 2p Imperfect

884 849 893 901 992

345 287 339 370 425

760 746 794 748 799

162 126 135 148 193

These results mirror those found by Cole´, Beauvillain, and Segui (1989) and Cole´, Segui, and Taft (1997) for derived words. The cumulative frequency effect is interpreted as evidence for storage of lexical items as ‘‘grouped’’ around a common root or stem (Taft, 1979). Both groups of subjects demonstrated a main effect of form in their RT data (F DLI (4, 0) ⫽ 3.9, p ⫽ .01; F C (4, 0) ⫽ 3.3, p ⫽ .02). RTs are plotted in Table 3. DLIs showed longer RTs on imperfect forms (F(1, 9) ⫽ 13.613, p ⬍ .01). Control participants showed longer RTs on the 2s and the imperfect forms (F(1, 9) ⫽ 12.636, p ⬍ .01). The longer RTs on the imperfect forms for the DLI participants might support a decompositional analysis for these items. However, other results speak against this analysis. The high error rate for these items indicates that even if they were using a decompositional route to access these forms, the process is not working. This is an unexpected result if they were using a productive morphological process. Furthermore, the DLI participants did not show the same patterns as control participants on the 2s form, which patterns like the imperfect for controls. We thus reject a decompositional analysis for the RTs on imperfect forms by DLI participants. CONCLUSION

These strongly diverging patterns for the two groups of subjects lead us to conclude that they are using qualitatively different linguistic processes to recognize words during a SLD task. The patterns of CRs and RTs found for controls showed that compound frequency and transparency interact during the word recognition process. In contrast, DLI participants seemed to be affected only by token frequencies. The fact that DLI participants were highly sensitive to surface frequencies points toward a full-listing type lexicon in these subjects. These results could be accounted for by a connectionist model which incorporates frequency and transparency effects (Daugherty & Seidenberg, 1994). However, a model which integrates factors such as irregularity within the verbal paradigm (i.e., presence of different stems for differ-

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ent forms) and token versus compound frequency has not yet been proposed. In addition, words of more than one syllable have not yet been modeled by these programs. It is also not clear how the pattern association model would account for regular inflection concurrent with irregular stem changes. Therefore, our results must be interpreted within the context of a model that accounts for morphological transparency, compound frequency and token frequency. Dual route models allow for this type of analysis.

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