Visual field effects for processing content and function words

Neuropsyrhologra, Vol. 25, No. Printed in Great Britain.

3, pp. 539-548.

1987 0

VISUAL FIELD

EFFECTS FOR PROCESSING FUNCTION WORDS CHRISTINE

Department

of Psychology,

CHIARELLO Syracuse

@_28-3932/87 $3.00+0.00 1987 Pergamon Journals Ltd.

CONTENT

AND

and SARAH NLJDING

University,

Syracuse,

NY 13244-2340,

U.S.A

(Received 24 June 1986; accepted 18 September 1986) Abstract-This study investigated the processing of content and function words when input to the left vs right hemispheres. For both lexical decision and naming there was a larger RVF advantage for function as compared to content words: function words were processed more slowly than content in the LVF, but not in the RVF. These results do not replicate the previous report of BRADLEY and GARRETT, Neuropsychologia 21, 155-159,1983, and provide some support for the view that function words are less accessible to the right hemisphere. In a second experiment, there was no difference in VF asymmetry when acceptability judgments were required for function vs content word phrases. Grammaticality judgments, of any sort, may be predominantly processed in the left hemisphere.

INTRODUCTION EVIDENCE from speech errors [ 133, aphasia [ 11,281, and acquired reading disorders [9,22] supports a dissociation between two major vocabulary classes, content (open class) and function (closed class) words. Content words are those that are rich in referential meaning, primarily nouns, verbs, and adjectives. Such forms are large in number, and are said to be part of an open class in that the language freely accepts additions to it. In contrast, function words convey primarily grammatical meaning, are few in number, and form a closed class not readily admitting new members. Conjunctions, prepositions, auxiliaries, pronouns and articles are examples of closed class items in English. It is well-known that processing of content vs function words can be separately disrupted after brain injury [l]. How should such content/function word dissociations be characterized in a language processing model? Based on a number of experimental findings from normal and aphasic individuals, BRADLEY et al. [4] have proposed that these word classes are accessed by fundamentally different mechanisms. Although some of these findings have not been replicable [12,15,16,23], the possibility of differential lexical access for these forms deserves serious consideration. In an evoked potential word recognition study GARNSEY [12] could find no evidence for differential access to content and function words, but did report processing differences which emerged subsequent to lexical access. She argued for differential post-access processing of content and function words, in the context of a uniform lexical access mechanism. While it has often been speculated that the right hemisphere is poorer at recognizing function than content words [lo], the information processing locus of such hemisphere differences has not been examined. In fact, there is only one published study which directly examines hemispheric processing of content and function words in normal individuals. BRADLEY and GARRETT [3], using a near-threshold naming task, reported differential recognition of these word classes in the right visual field (RVF), but not in the left visual field 539

540

CHRISTINE CH~ARELLOand

SARAHNUDING

(LVF). While accuracies for content and function words were equivalent in the LVF, content words were much more accurately named than function words in the RVF. Surprisingly, the overall RVF advantage for the task was greater for content than for function words. Based on these results, Bradley and Garrett argued that a specialized retrieval mechanism for function words was only available to the left hemisphere. These findings are remarkable for two reasons. First, the greater asymmetry for content word recognition contradicts the view of the right hemisphere as being relatively asyntactic [lo, 271. Since function words convey primarily grammatical meaning, this view would predict diminished LVF/RH (right hemisphere) performance, and thus a greater RVF/LH advantage for function as opposed to content words. While this conventional interpretation may be inaccurate, further experimentation is warranted. Second, if the left hemisphere utilizes a specialized access mechanism for function words, it is unclear why this should result in better content than function word recognition in the RVF. If different mechanisms are being used, one would expect access to the smaller, closed class to operate more efficiently than access to a vocabulary which includes the larger, open class.* In the current study we attempted to replicate BRADLEY and GARRETT’S [3] result, and investigated whether content/function word processing differences might be attributed to differential lexical access or post-access processing. In Experiment 1 we compared VF asymmetries for content and function words using lexical decision and naming tasks. To the extent that both tasks require access to lexical representations [26], similar results would be expected across tasks if lexical access mechanisms account for content/function word differences.+ However, if dissociable content/function word asymmetries are present for naming, but not lexical decision, this would suggest that it is access to speech production, and not access to a lexical representation, which differs for these word classes across the hemispheres. In addition, if only the left hemisphere utilizes specialized mechanisms for accessing content and function words [3], these items should be differentially processed in the RVF, but not the LVF. On the other hand, if the right hemisphere is selectively deficient in function word recognition, such forms should be processed less well than content words in the LVF, but not the RVF. In Experiment 2 we compared acceptability judgments for function vs content word phrases. Because such judgments require substantial post-access processing, the results for this task will serve as a useful counterpoint to findings from Experiment 1. If content and function words are differentially processed only after lexical access, then we should observe a much more robust content/function word dissociation in Experiment 2 than in Experiment 1.

EXPERIMENT

1

Method Subjects. Forty-eight credit for participating

right-handed native English speaking undergraduates (24 female, 24 male) received course in the study. All had normal vision, and none had any left-handed immediate family

*BRADLEY and GARRETT 131 have argued that function words are “less available for report” in the left hemisphere because they are pre-empteh by the syntactic parser. While interesting, there is no subsiantiating evidence fdr this conjecture. TWe assume here, following SEIDENBERG [24], that lexical access involves activation of all information associated with a word (i.e. orthographic, phonological, and semantic codes).

VISUAL FIELD EFFECTSFOR PROCESSINGCONTENT AND FUNCTION WORDS

541

members. Handedness was assessed using a five-item hand preference questionnaire [6] which yields an index ranging from + 1.OO (extreme right-handedness) to - 1.00 (extreme left-handedness). All participants had an index of at least +0.30 (mean = f0.80). Twenty-four subjects were assigned to the lexical decision task and 24 to the naming task. Each task group was balanced by sex. Stimuli. Stimuli consisted of 30 content and 30 function words matched for length (mean =4.1) and log frequency (mean=2.67, range = 1.83 to 3.10) [20]. As in previous investigations [2, 12, 151, the log frequency for each item was summed over the regularly inflected forms listed in KUCERA and FRANCIS [20]. The stimuli were a subset of those employed by GARNSEY 1123 in which nouns, verbs, and adjectives were classified as content words, while pronouns, auxiliary verbs, quantifiers, conjunctions, prepositions, articles, and some non-‘ly’ adverbs were considered function words. These stimuli are listed in the Appendix. In addition 60 nonword stimuli were constructed for the lexical decision task by changing one letter of a real word. The resulting nonwords were pronounceable, orthographically “legal”, nonhomophonic to real words, and matched for length to the word stimuli. Stimuli were horizontally presented in upper case, and subtended 1.4 to 2.4” of horizontal visual angle, and 0.39” of vertical visual angle. The center ofeach string was positioned 2.8” from the central fixation marker. Each stimulus appeared once in each visual field. Apparatus andprocedure. Subjects were seated in a sound-attenuated room 175 cm in front ofa Hewlett-Packard 1310B vector graphics display equipped with a fast decay phosphor. The display and a condenser microphone (Realistic 33-1050A) were interfaced to an LSI 1 l/23 computer which controlled stimulus presentation and timing and recorded subjects’ responses. Background luminance was 1.46 mL, background + test luminance 2.32 mL. A modified Tectronics viewing hood was used to stabilize head position, while still allowing the subject to vocalize freely. Each trial was initiated by a 50 msec 3.75 KHz warning tone and simultaneous presentation of a centrally displayed “ +“. When the fixation cross had been shown for 500 msec, the stimulus appeared, randomly to the left or right visual field. The cross remained visible for 200 msec after stimulus offset. Pilot testing revealed that, in order to obtain equivalent accuracy across tasks, briefer exposures were necessary for naming. For this reason stimuli appeared for 35 msec for naming, but 100 msec for lexical decision. We felt it was necessary to equate accuracy across tasks in order to allow the possibility of obtaining wordclass x VF accuracy interactions in each task (since BRADLEY and GARRETT [S] reported only accuracy data). With our stimuli, naming accuracies at 100 msec approached 90%, while lexical decisions were nearly at chance at 35 msec. Thus, in order to avoid ceiling/floor effects for both tasks (which might preclude interpretable VF interactions, see [18], different exposure times were required. Each task began with practice trials (30 for naming, 40 for lexical decision), followed by two experimental blocks (60 trials each for naming, 120 trials each for lexical decision) separated by a rest period. Stimuli were repeated in the second block but with visual field of presentation reversed. Stimuli were independently randomized for each subject, with the restriction that no more than three successive trials appear in the same visual field. Subjects were informed that the experiment investigated how well individuals could recognize stimuli they were not directly looking at, and were instructed to maintain their gaze on the central cross as long as it was visible. For naming, subjects were told to pronounce each word as quickly and accurately as possible, guessing if necessary. Vocal reaction times, measured from stimulus onset, were automatically recorded. In addition, the experimenter (who was in a separate room monitoring performance via headphones) entered any error responses into the computer for later analysis. In the case of spurious vocal responses (a cough for example), a zero was entered, and such trials were not analyzed. Less than 1% of the trials were discarded for this reason. The next trial was initiated 4.5 set after the subject’s response. In the lexical decision task subjects were instructed to register their word/nonword decisions by pressing one of two response keys as quickly and accurately as possible. * “Word” responses were made with the index finger and “nonword” responses with the middle finger of the right hand. Accuracy of response and reaction time, measured from stimulus onset, were recorded online.

Results Since preliminary analyses ruled out any reliable effects attributable to Sex, percent correct scores and median reaction times were analyzed via mixed design analyses of variance, examining the variables Task, Wordclass, and VF. The relevant means are shown

*An anonymous reviewer suggested that recording vocal lexical decision latencies might have been more comparable to naming responses. We have recently obtained data on right-hand manual and vocal (yes/no) lexical decisions and found quite similar RT results: LVF: manual 797 msec, vocal 803 msec; RVF: manual 726 msec, vocal 727 msec. Thus, it is unlikely that the results of the present study would have differed had we employed vocal lexical decisions.

CHRISTINECHIARELLO and SARAH NUDING

542

in Table 1. Following BRADLEY and GARRETT [3], both subject and item analyses were computed. In the former, subject means are collapsed over items, while in the latter item means are collapsed over subjects. This allows us to determine whether the effects are generalizable over subjects as well as items. Table 1. Mean reaction times and percent correct by Task, Wordclass, and VF (Experiment 1) Lexical decision LVF RVF

Content Function Content Function

Reaction time 678 673 699 669 Percent correct 78.6 86.9 13.3 82.4

Naming LVF RVF

683 694

657 641

75.7 74.0

87.0 84.7

For

reaction times a main effect of Visual Field was obtained over subjects, 17.46, P 0.20: in lexical decision content words were recognized somewhat faster than function words, while the opposite pattern occurred in naming. Finally, a Wordclass x VF interaction was obtained in the subject analysis, F (1,46) = 4.31, P < 0.05, but was not reliable over items (F-c 1). Post-hoc analyses indicated that in the LVF function words were recognized more slowly than content words, F (1,92) = 4.15, P < 0.05, while in the RVF no wordclass effects were obtained, P>O.20. The RVF advantage was significant for function words, F (1,92) = 20.17, P < 0.001, and marginally significant for content words,

F (1,46)=

F(1,92)=2.92, P=O.O9. For

accuracy

scores,

we obtained

a main

effect

of Visual

Field,

over

subjects

F (1,46) = 48.23, P < 0.0005, and over items, F (1, 58) = 69.43, P < 0.0005. In addition, there was a main effect of Wordclass in the subject analysis, F (1,46) = 19.16, P < 0.0005, but this was not reliable over items (F-c 1): errors were more frequent for function words, a result also reported by BRADLEY and GARRETT [3]. No other effects reached significance. For the naming task, we also examined error patterns in each VF separately for content and function word stimuli. Each error response was classified as a function or content word. Less than 1% of the errors were unclassifiable (e.g., “ouch”) and not included in the analysis. Separate repeated measures analyses of variance were conducted for content and function word stimuli examining the variables of VF and error response (content or function word). Forfunction word stimuli, there were main effects of VF, F (1,23) = 21.97, P < 0.0005, and Error Response, F (1, 23) = 15.80, P < 0.0005, but no interaction (F< 1). There was a bias to respond with a content word when a function word was not correctly named, but this bias was present to an equivalent extent in both VFs. For content word stimuli, there were again main effects of VF, F (1,23)= 15.19, P
VISUAL

FIELD

EFFECTS

FOR PROCESSING

of VF or stimulus type. However, this response when content words were presented.

CONTENT

AND FUNCTION

bias was especially

WORDS

pronounced

543

in the LVF

DISCUSSION Our findings can be succinctly summarized. We were unable to replicate, in either lexical decision or naming, the results reported by BRADLEY and GARRETT [3]. We did not obtain wordclass effects in the RVF, nor did we find a greater RVF advantage for recognizing content words. Thus the results offer no support for the view that content and function words are differentially accessed only in the left hemisphere. However, we did find some evidence (albeit weak) for a function word deficit for stimuli input to the right hemisphere. While function and content words were recognized with equivalent speed in the RVF, function words were recognized more slowly than content items in the LVF; thus a greater RVF advantage for processing function as opposed to content words. Although this result is consistent with the conventional view of the “asyntactic” right hemisphere, we would urge some caution in interpretation. The critical interaction was only obtained for response time, and not accuracy, and the RT effect was reliable over subjects, but not items. This suggests that our results might not be generalizable to the entire population of content/function words (although we would expect the results for this stimulus list to be replicable with another group of subjects). We will consider this issue further after reporting the results of a final experiment. It has been suggested that, since naming requires a vocal response, larger RVF advantages should be obtained for this task in comparison to the nonvocal lexical decision [S]. Although there is some suggestion of such an effect in our RT results (see Table I), the critical interaction did not approach significance. It may be that a within-subjects design is necessary in order to demonstrate such effects. Our failure to find task differences might be attributable to the different exposure times used. However, the size of the RVF advantage in word recognition tasks is typically stable over a range of exposure times [S]. In any case, no task differences were observed in the present study. It might be argued that word recognition tasks, such as lexical decision and naming, may not be the most sensitive measures of hemisphere differences in processing function vs content words. Regardless of whether or not these words are differentially accessed, it is clear that they have very different roles in sentence and phrasal contexts. In order to investigate possible hemisphere differences in such post-access processing of content and function words, we developed a simple phrase judgment task. Subjects were presented with a twoword sequence and were asked to judge whether or not it was a possible English phrase. Half of the phrases contained two content words (ASK ADVICE; ASK BEGINS) and half contained a function and content word (EVERY HOUR; EVERY HEAR). If the right hemisphere is selectively deficient in post-access processing of function words, then the latter phrases should be less well processed than the former when the stimuli are shown in the LVF.

EXPERIMENT

2

Method Subjects. Subjects were the same 24 individuals who participated in the lexical decision task reported above. Half performed the phrase judgment task before lexical decision, and half after. The two testing sessions were separated by at least 3 days.

544

CHRISTINE CHIARELLO and SARAH NUDING

Stimuli. The stimuli included 80 two-word phrases, 40 consisting of two content words (content phrases) and 40 consisting of a function and content word (function phrases). Half of each group were impermissible English sequences (bad phrases) and half were “legal” phrases (good phrases). Potentially lexicalized collocations were avoided. The entire stimulus list is given in the Appendix. As indicated in Table 2, content and function stimuli were selected so as to be comparable in length and log frequency 120). In addition, 20 undergraduate native English speakers used a 7-point scale to rate the extent to which these phrases were grammatical and “made sense”. Content and function phrases were rated equally good (or bad), and the good and bad phrases were judged to be markedly different in acceptability (see Table 2). Finally, a second group of 10 undergraduates made binary decisions about the acceptability of these phrases. There was over 95% agreement on our classification of good vs bad phrases. This indicates that with free viewing there is little or no ambiguity in correctly classifying these phrases.

Table 2. Stimulus

Word

Length Log Freq. Phrase rating Length Log Freq. Phrase rating

characteristics-Experiment Content 1 Word 2

Good phrases 4.15 5.20 2.16 1.78 -5.48-Bad phrases 4.15 5.25 2.76 1.78 ---2.48--

Word

2

Function 1 Word 2

4.25 2.77 ---5.37---

5.40 1.76

4.25 2.17 --2.4L

5.35

1.71

Procedure. Apparatus was the same as that used in Experiment 1. Trials were initiated with the warning tone and simultaneous presentation of the fixation marker. After 500 msec had elapsed the first word was displayed for 100 msec, randomly to the LVF or RVF. Approximately 8 msec later the second word appeared in the same VF in a position below the first word for 100 msec. The fixation cross remained visible for an additional 200 msec. The succeeding trial began 1.2 set after a response was registered. As in the previous experiment, words were horizontally displayed and centered 2.8” from the fixation marker. The session consisted of40 practice trials, followed by two experimental blocks of 80 trials each. The second block contained the same stimuli as the first, but with visual field reversed. Stimuli were independently randomized for each subject, with the restriction that no more than three successive trials should appear in the same visual field, or be of the same response type. Fixation instructions were as described earlier. Subjects were instructed to register their phrase judgments as quickly and accurately as possible by pressing response buttons with the index (good phrase) or middle (bad phrase) finger of their right hand. Good phrases were defined as those which were grammatical and made sense, although not necessarily forming a complete sentence. Bad phrases were defined as ungrammatical, and not expressing a complete thought or idea. Both accuracy of response and reaction time, measured from onset of the second word, were recorded online.

Results Median RTs and percent correct scores were analyzed with repeated measures (over subjects) and mixed design (over items) ANOVAs, examining the variables Phrase Type (good, bad), Wordclass, and VF. The means are given in Table 3. For response times, there was a main effect of Phrase Type over subjects F (1,23) = 78.83, P-c0.0005, and items, F (1, 76) = 53.12, P < 0.0005: good phrases were classified approximately 100 msec faster than bad phrases. There was only a marginal RVF advantage in the item analysis, F (1, 76) = 3.03, P-c0.09, but not in the subject analysis, P>O.20.None of the interactions, including the critical Wordclass x VF contrast, even approached significance (all P’s >0.25). For accuracy, the only finding was a main effect of VF, over subjects F (1,23)= 11.72, P < 0.001, and items, F (1,76) = 22.63, P < 0.0005. There were no significant interactions.

VISUAL

FIELD

EFFECTS

FOR PROCESSING

CONTENT

AND FUNCTION

WORDS

545

Table 3. Mean reaction times and percent correct by Phrase Type, Wordclass, and VF (Experiment 2) Good phrase LVF RVF

Bad phrase LVF RVF

Reaction time

Content Function

798 765

Content Function

76.3 76.5

759 768

882 887

865 881

80.0 80.8

85.6 83.3

Percent correct

84.0 82.7

DISCUSSION In Experiment 2 content and function phrase acceptability judgments were not differentiated in either VF. The slight processing deficit for LVF function words observed in both word recognition tasks was not obtained when the task required syntactic-semantic integration in a phrasal context. Thus we could find no evidence for a selective LVF deficiency for phrase judgments involving function words, nor for an enhanced content/function dissociation for post-access processes [ 121. Phrase judgments were more accurate and somewhat faster in the RVF with no demonstrable effect of Wordclass. It is possible that our failure to find Wordclass effects reflects the metalinguistic nature of this task. Online measures of syntactic processing may be required to demonstrate such effects [12]. Before interpreting the collective results of the current experiments, we need to consider possible reasons why we failed to replicate the earlier report of BRADLEY and GARRETT [3]. Mean word length and frequency were comparable across the two studies, as were the number of trials and general experimental procedure. However, since Bradley and Garrett did not publish their stimulus list, we cannot determine how similar the items were across studies. In their study independent thresholds were set for each subject to allow approximately 50% correct identifications, while overall performance in the current study was 80% correct. This raises the possibility that LVF wordclass effects could have been truncated in the former investigation, although it is difficult to estimate a theoretical floor for naming performance. Finally, Bradley and Garrett did not record RTs, while we observed the LVF function word deficit only for response times. These procedural differences limit the extent to which the studies can be directly compared. Any of the above discrepancies may have contributed to the conflicting findings. In addition, there is reason to suspect that the particular stimuli (both content and function) selected for each study may have influenced the results. GORDON and CARAMAZZA [ 171 recently reported word-specijc influences on lexical decision latencies for both content and function words. Reliable differences in item means were found across four studies even though the words were equated for frequency, length, number of syllables, and wordclass. This suggests that intrinsic word variability may be substantial even among “well controlled” stimulus sets, which would hinder replicability when independent samples of items are used. In a related vein, several researchers have pointed out that the class of function words is quite heterogeneous with respect to semantic and logical content, syntactic roles, and stress [14, 191. Dissociations within the class of content words are also present: agrammatic aphasics are deficient in producing main verbs as opposed to nouns [7,21]. As GOODGLASS and MENN [ 141 note, the content/function distinction is at best a “first-pass dichotomy”. To

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CHRISTINE CHIARELLO and SARAH NUDING

date, the collective lateralization results suggest that this global distinction may not adequately capture lexical processing differences across the hemispheres. More subtle syntactic/semantic distinctions are only partially subsumed under the content/function dichotomy, and thus may not have been consistent across studies. Further investigations, considering sub-types of content and function words, are obviously needed. Although we remain cautious about overgeneralizing our results, the findings of the present study are consistent with the bulk of previous research on lexical access for content and function words. Most investigations find no evidence for content/function dissociations in word recognition [ 12,15-17,251, a result which characterizes our RVF naming and lexical decision times. The function word deficit which we observed for LVF stimuli is compatible with the view that the right hemisphere is better equipped to process semantic rather than grammatical aspects of meaning. Because this finding was observed for both lexical decision and naming tasks, it points to a dissociation in lexical access rather than to post-lexical decision or pronunciation processes. However, we suggest that the content/function dichotomy may not be the best cover term to capture hemisphere differences in lexical processing, and future studies should focus on less global distinctions. The absence of any reliable wordclass effects in the phrase judgment task precludes interpretation of hemisphere differences in post-access processing of content vs function words. There was no evidence of qualitative VF differences in this task, unlike the results for word recognition. Given the overall RVF advantage fof phrase judgments, the simplest interpretation would posit that the left hemisphere plays a predominant part whenever grammaticality judgments are required. The presence of a LVF function word deficit for word recognition, but not phrase judgments, is compatible with this view. In conclusion, we found no support for BRADLEY and GARRETT’S [3] conjecture that the left hemisphere utilizes a specialized access mechanism for function words. In both lexical decision and naming, function words were recognized more slowly than content items only when presented in the LVF. No wordclass effects were found for RVF stimuli. This is suggestive of a right hemisphere deficit in accessing at least some function words. While the content/function word distinction has proven to be a useful heuristic, we suggest that future lateralization research focus on teasing out the various semantic and syntactic distinctions subsumed under this global dichotomy. Acknowledgments-This research was supported by BSRG Grant 2 SO7 RR077068-19. We thank Susan Garnsey for providing us with a copy of her stimulus list, and Paul Gelling for programming assistance. Curt Burgess and Susan Garnsey also provided helpful comments on the manuscript.

REFERENCES 1. BERNL)T, R.S. and CARAMAZZA, A. Syntactic aspects of aphasia. In Acquired Aphasia, M. T. SARNO (Editor). Academic Press, New York, I98 I. 2. BRADLEY, D. C. Computational distinctions of vocabulary type. Ph.D. dissertation, MIT, 1978. 3. BRADLEY, D. C. and GARRETT, M. F. Hemisphere differences in the recognition of closed and open class words. Neuropsycholcyia 21, 155-159. 1983. 4. BRADL.EY,D. C., GARKETT, M. F. and ZURIF, E. B. Syntactic deficits in Broca’s aphasia. In Biological Studies of MenralProcesses, D. CAPLAN (Editor). MIT Press, Cambridge, 1980. 5. BRADSHAW, J. L. and GATES, E. A. Visual field differences in verbal tasks: effects of task familiarity and sex of subject. Brain Lang. 5, 166187, 1978. 6. BRYDEN, M. P. Laterality: Functional Asymmetry in the Intact Brain. Academic Press, New York, 1982. 7. CARAMAZZA, A. and BERNDT, R. S. A multicomponent view of agrammatic Broca’s aphasia. In Agrammatism, M. KEAN (Editor). Academic Press. Orlando. 1985.

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8. CHIARELLO, C. Lateralization 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24.

25. 26. 21. 28.

of lexical processes in the normal brain: a review of visual half-field research. H. A. WHITAKER (Editor), Contemporary Reviews in Neuropsychology, Springer-Verlag, New York, in press. COLTKEART, M. Deep dyslexia: a review of the syndrome. In Deep Dyslexia, M. COLTHEART, K. PATTERSONand J. MARSHALL (Editors). Routledge & Kegan Paul, London, 1980. COLTHEART, M. Deep dyslexia: a right-hemisphere hypothesis. In Deep Dyslexia, M. COL.THEART, K. PATTERSON and J. MARSHALL (Editors). Routledge & Kegan Paul, London, 1980. FRIEDERICI, A. D. Levels of processing and vocabulary types: evidence from on-line comprehension in normals and agrammatics, Cognition 19, 133-166, 1985. GARNSEY, S. M. Function words and content words: reaction time and evoked potential measures of word recognition. Cognitive Science Technical Report. University of Rochester 29, 1985. GARRETT, M. F. Levels of processing in sentence production. In Language Production I, B. BUTTERWORTH (Editor). Academic Press, New York, 1980. GOODGLASS, H. and MENN, L. Is agrammatism a unitary phenomenon? In Agrammatism, M. KEAN (Editor). Academic Press, Orlando, 1985. GORDON, B. and CARAMAZZA, A. Lexical decision for open- and closed-class words: failure to replicate differential frequency sensitivity. Brain Lang. 15, 143-160, 1982. GORDON. B. and CARAMAZZA, A. Closed- and open-class lexical access in agrammatic and fluent aphasics. Brain Lang. 19,335-345, 1983. GORDON, B. and CARAMAZZA, A. Lexical access and frequency sensitivity: frequency saturation and open/closed class equivalence. Cognition 21, 95-115, 1985. HELLIGE, J. B. Hemisphere x task interaction and the study of laterality. In Cerebral Hemisphere Asymmetry: Method, Theory, and Application, J. B. HELLIGE (Editor). Praeger, New York, 1983. KEAN, M. Grammatical representations and the description of language processing. In Biological Studies of Mental Processes, D. CAPLAN (Editor). MIT Press, Cambridge, 1980. KUCERA, H. and FRANCIS, W. N. Computational Analysis ofPresent-day American English. Brown University Press, Providence, 1967. MICELI, G., SILVERI, M. C., VILLA, G. and CARAMAZZA, A. On the basis for the agrammatics difficulty in producing main verbs. Cortex 20, 207.-220, 1984. MORTON, J. and PATTERSON, K. “Little words-No!” In Deep Dyslexia, M. COLTHEART, K. PATTERSONand J. MARSHALL (Editors). Routledge & Kegan Paul, London, 1980. SEGUI, J., MEHLER, J., FRAUENFELDER, U. and MORTON J. The word frequency effect and lexical access. Neuropsychologia 20, 615428, 1982. SEIDENBERG, M. S. The time course of information activation and utilization in visual word recognition. In Reading Research: Adtiances in Theory and Practice, Vol. 5, D. BESNER, T. G. WALLER and G. E. MACKINNON (Editors). Academic Press, Orlando, 1985. SEIDENBERG, M. The time course of phonological code activation in two writing systems. Cognition 19, l--30, 1985. SEIDENBERG, M., WATERS, G. S., SANDERS, M. and LANGER, P. Pre- and postlexical loci of contextual effects on word recognition. Memory and Cognition 12, 315-328, 1984. ZAIDEL, E. On multiple representations of the lexicon in the brain-the case of two hemispheres. In Psychobiology ofLanguage,M. STUDDERT-KENNEDY (Editor). MIT Press, Cambridge, 1983. ZURIF, E. B. and CARAMAZZA, A. Psycholinguistic structures in aphasia: studies in syntax and semantics. In Studies in Neurolinguistics, Vol. 1, H. WHITAKER and H. A. WHI~AKER (Editors). Academic Press, New York, 1976.

APPENDIX Word stimuli-Experiment

1

Content words: come, day, doubt, easy, fall, feel, gain, great, good, jump, long, look, make, own, point, power, sale, see, sense, set, staff, stop, study, talk, today, unite, use, way, wide, work Function words: after, again, among, aside, below, did, does, done, each, else, ever, every, few, how, less, many, maybe, most, much, must, nor, over, shall, soon, such, those, too, whom, yet, your Stimuli-Experiment

2

Good phrases. Content: act guilty, ask advice, close doors, cause stress, clear choice, find toys, gain money, great mayor, high score, know French, life begins, long walk, look strong, order food, play sports, reach goals, see smoke, seem tired, turn pages, want kids. Function: after summer, both levels, does listen, every hour, few spots, how funny, least severe, many cities, much noise, must agree, often drunk, quite pretty, shall stay, since Friday, too proud, until today, upon waking, very bitter, while eating, why argue

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CHRISTINE CHIARELLO and SARAH NUDING

Bud phrases. Content: act argued, ask begins, close dirty, cause expect, clear write, find warn, gain leaned, high aside, know using, life motor, long meant, look stood, order moral, play listen, reach writes, seem swung, turn reveal, want weak. Function: after showed, both relief, does alive, every hear, few latest, least decide, many middle, much forty, must dozen, often camera, quite rates, shall heavy, since avoid, until tell, upon louder, very create, while pencil, why mines

seen, great see decide, how porch, too foods,