VA Merit Review from the VA Research Council to William Milberg. Thanks to Shari ... of words. Goodman, McClelland and Gibbs (1981) demonstrated that.
BRAIN
AND
LANGUAGE
40,
393-421 (1991)
Syntactic Priming Effects in Aphasia: An Investigation of Local Syntactic Dependencies SHEILA E. BLUMSTEIN Brown
University
and Aphasia
Research
WILLIAM Aphasia
Research
Center,
Boston
Center,
Boston
VA Medical
Center
P. MILBERC
VA Medical
Center,
and GRECC,
VA Medical
Center
BARBARA DWORETZKY Brown
University
and Aphasia
Research
ALLYSON Brown
University
and Alphasia
Research
Center,
Boston
VA Medical
Center
Boston
VA Medical
Center
Boston
VA Medical
Center
ROSEN Center,
AND FELICIA GERSHBERG Brown
University
and Aphasia
Research
Center,
This study explored on-line processing of local syntactic dependencies in normal subjects and in Broca’s and Wernicke’s aphasics using a lexical decision paradigm. In addition, subjects performed a grammaticality judgement task on the real word pairs used in the lexical decision tasks. Results of two experiments for normal subjects indicated different syntactic priming effects as a function of the type of local syntactic dependency. Word pairs that formed a single constituent phrase, This research was supported in part by Grants DC00314 to Sheila Blumstein at Brown University, DC0081 to Harold Goodglass at Boston University School of Medicine, and by VA Merit Review from the VA Research Council to William Milberg. Thanks to Shari Baum for her help in testing patients and to Pauline Jacobson for discussions on issues relating to local syntactic dependencies from both a theoretical and a processing point of view. Address correspondence and reprint requests to Sheila E. Blumstein, Brown University, Department of Cognitive and Linguistic Sciences, Box 1978, Providence, RI 02912. 393 0093-934x/91 $3.00 Copyright Q 1991 by Academic Press, Inc. All rights of reproduction in any form reserved.
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ET AL.
i.e., a verb phrase, showed both facihtory and inhibitory effects, whereas word pairs that reflected local syntactic dependencies across a phrase boundary, i.e., pronoun verb, showed only inhibitory effects. Broca’s aphasics failed to show facilitory effects when presented with word pairs forming a single constituent phrase but, similar to normals, did show inhibition when presented with word pairs that reflected local syntactic dependencies across a phrase boundary. In contrast, Wernicke’s aphasics failed to show inhibitory effects in both experiments. The implications of these results for theories of language processing deficits in aphasia are considered. o 19% Academic press, h.
There have been a number of attempts to characterize the syntactic impairments in the auditory comprehension of agrammatic Broca’s aphasics. Several hypotheses have been proposed attributing agrammatism to various types of disturbances including: impairments in the closed class vocabulary (Zurif, Caramazza, & Myerson, 1972; Goodglass & Menn, 1985; Grodzinsky, 1984); a failure to use the closed class vocabulary as input to the parser (Bradley, Garrett, & Zurif, 1980); a phonological deficit affecting nonphonological words or clitics (Kean, 1980); a deficit in the syntactic parser (Berndt & Caramazza, 1980); and a syntactic mapping deficit reflecting a failure to exploit syntactic representations for the purpose of semantic interpretation (Linebarger, Schwartz, & Saffran, 1983; Caplan, Baker, & Dehaut, 1985). A number of difficulties have emerged in evaluating these various theories. First, performance of the patients is rarely “all or none,” as seems to be implied by a number of these models. For example, several studies have shown that even though agrammatic patients seem to have an impairment in processing morphological structure, they are indeed sensitive to inflectional morphology in highly inflected languages (Heeschen, 1980; Smith & Mimica, 1984; Friederici, 1983, 198.5; Kolk & Van Grusven, 1984; Smith & Bates, 1987; Lukatela, Crain, & Shankweiler, 1988). Second, performance of patients has been inconsistent across the various experimental paradigms used in these studies. Thus, agrammatic aphasics who demonstrated impairments in sentence comprehension tasks nonetheless were able to perform complex grammaticality judgements (Linebarger et al., 1983). One possible contributing factor to these apparent contradictory findings is the variation in the experimental methods used in testing aphasic patients. Most of the experiments have explored sentence comprehension by requiring the patient to make an overt decision (e.g., picture pointing, toy manipulation, grammatical judgement) after the test stimulus has been presented-in other words, after sentence processing has been completed. While these methods provide data about patients’ success or failure to comprehend sentences and their sensitivity to certain types of sentences or morphological markers, they do not provide insight into the many processes potentially contributing to sentence comprehension. It is pos-
SYNTACTIC
PRIMING
IN APHASIA
395
sible that common patterns of performance on sentence comprehension tasks could reflect impairments in different underlying processing mechanisms. On-line tasks therefore provide a useful method for exploring language processing capacities. On-line tasks have proven valuable in the study of language processing in normals (cf. Tanenhaus, Carlson, & Seidenberg, 1985). Investigations focussing on normal subjects’ sensitivity to grammatical structure have shown that local syntactic dependencies or syntactic relations may be used to facilitate lexical access and in particular the recognition and processing of words. Goodman, McClelland and Gibbs (1981) demonstrated that lexical decision latencies are shorter when a word is preceded by another word producing a syntactically legal phrase (e.g., men swear) than when the target word is preceded by a word producing a syntactically illegal phrase (e.g., whose swear). Lukatela, Kostic, Feldman, and Turvey (1983) showed that in Serbo-Croatian, lexical decision latencies to noun targets were faster when the preceding preposition agreed in case. In addition, Wright and Garrett (1984) found that the grammatical structure of sentence fragments affected lexical decision latencies to various final word targets, even though the targets were not semantically related to the preceding context and the sentence fragments were semantically anomalous. Finally, Caramazza, Laudanna, and Romani (1988) showed that even lexical decisions to nonwords are affected by the morphological structure of the stimuli. Thus, the presence of local syntactic constraints can alter the speed and efficiency of lexical access. Central to most claims concerning agrammatism is the specificity of these deficits to Broca’s aphasics. A number of studies using either a picture-pointing paradigm (Goodglass, 1968; Lesser, 1978; Parisi & Pizzamiglio, 1970; Shewan & Canter, 1971; Shewan, 1976; Naeser, Mazurski, Goodglass, Peraino, Laughlin, & Leaper, 1987; Blumstein, Dworetzky, & Engen, 1989) or a toy manipulation paradigm (Caplan et al., 1985) have shown that other types of patients including Conduction, anemic, and Wernicke’s aphasics display patterns of performance similar to those of Broca’s aphasics. In these studies, the test materials included sentences varying in morphological structure, syntactic structure, and syntactic complexity. Thus, while it is clear that Broca’s aphasics may have syntactic impairments, it is not clear how their deficits differ from those of other aphasics (cf. Caplan et al., 1985). The aim of the current study was to explore whether similar sensitivities to syntactic structure emerge in Broca’s and Wernicke’s aphasics. To this end, we have focussed on the role of morphological structure in relation to local syntactic dependencies. Local syntactic dependencies can be defined in terms of the functional role words play with respect to the phrase structure of the sentence. Some local dependencies are defined within a syntactic phrase. For example, the auxiliary “have” and the modal “can”
396
BLUMSTEINETAL.
require particular stems on the main verb of the sentence. The aux, modal, and main verb are part of the same constituent phrase, the verb phrase. In contrast, other local dependencies are defined across phrase boundaries. For example, the subject pronoun requires agreement in person and number with the verb of the sentence. These syntactic dependencies cross phrasal boundaries, as the subject pronoun is part of the noun phrase and the verb is part of the verb phrase. In both examples, two contiguous words share syntactic dependencies, and these dependencies govern the morphological markers used. In one case, however, these dependencies are governed within a constituent phrase, and in the other they are governed across constituent phrases. In this study, we will explore whether the nature of local syntactic dependencies contributes to the patterns of performance for both normal and aphasic subjects. It is also important to determine the nature of the processes contributing to these syntactic effects. Research with normals has suggested that there are two distinct types of processing that occur during lexical access--one that is fast acting, effortless, is not under the subject’s control, does not demand attentional resources, does not interfere with other tasks, and is not strategic (called automatic processing), and another that is slow acting, effortful, under the subject’s voluntary or conscious control, uses attentional resources, and interferes with other tasks (called controlled processing) (Posner & Snyder, 1975; Shiffrin & Schneider, 1977; Neely, 1976). While the dichotomy between automatic and controlled processing has been developed largely with respect to lexical access, there is the possibility that this division between involuntary/rapid/unconscious processes and voluntary/slow/conscious processes may underlie syntactic processing as well. Conceivably, the rules that govern the relationships between contiguous words in a sentence may be accessed automatically, they may be accessed via a direct controlled search of possible alternatives, or they may be accessed via some combination of these processes. In the experiments described above (Goodman et al., 1981; Lukatela et al., 1983; Wright & Garrett, 1984), lexical decision latencies for grammatically permissible phrases were shorter than lexical decision latencies for grammatically nonpermissible phrases. However, it is not clear from these studies whether this so-called syntactic priming effect is due to facilitory processes, inhibitory processes, or a combination of the two. In the absence of a neutral baseline condition (i.e., one which neither facilitates nor inhibits lexical access), it is impossible to determine what processing mechanisms are contributing to the differences in reaction-time latencies between grammatical and ungrammatical stimuli. The only study that directly compared lexical decision latencies for syntactically correct and incorrect phrases to a neutral baseline was Goodman et al. (1981). They found longer reaction-time latencies for syntactically inappropriate word pairs relative to the baseline and no difference in reaction times for
SYNTACTIC
PRIMING
IN APHASIA
397
syntactically appropriate word pairs relative to the baseline. On the basis of these findings, Goodman et al. concluded that syntactic priming is due to inhibitory processes, i.e., processes that involve conscious strategies of the listener. In sum, the current study explored the sensitivity of Broca’s and Wernicke’s patients to local syntactic dependencies, particularly as they reflect morphological structure. We investigated local syntactic dependencies within a phrase (Experiment I) and local syntactic dependencies between phrases (Experiment II) using a lexical decision paradigm that has previously been shown to be sensitive to the processing of semantic relationships between words in aphasic patients (Milberg & Blumstein, 1981; Blumstein, Milberg, & Shrier, 1982). We also attempted to determine whether syntactic priming effects are facilitory, inhibitory, or a combination of the two. The dichotomy between automatic and controlled processing serves in the current research as an organizing construct. The results of the current experiment do not rest specifically on this dichotomy nor will they settle the issue of the nature of the processing deficits in aphasia. However, they will provide a useful heuristic for exploring potential syntactic processing impairments in aphasia, particularly as they relate to local syntactic dependencies. To approach the issue of the routines underlying syntactic processing, we will compare performance of subjects on the various experimental conditions to the neutral baseline condition. In particular, consistent with earlier research (Neely, 1976, 1977; Goodman et al., 1981), facilitation, i.e., faster reaction time relative to the neutral baseline condition, is interpreted as invoking either automatic or controlled processing, whereas inhibition, i.e., slower reaction time relative to the neutral baseline condition, is interpreted as invoking primarily controlled processing routines. Following the logic of Posner and Snyder (1975), we assume that facilitation exclusively reflects automatic processing when inhibition is absent, and reflects some combination of automatic and controlled processing when inhibition is observed. Critical to this argument is performance relative to a neutral baseline. The literature of the last few years has recognized a number of problems in identifying “neutrality” vis B vis the lexical decision paradigm. Neutrality of the prime is interpreted to mean “semantically” neutral and presumably “strategically” neutral with respect to the target. The complex issues surrounding the selection of neutral primes are beyond the scope of the current paper (see for example den Heyer, Taylor, & Abate, 1986), but each possibility has advantages and disadvantages particularly when applied to patients with brain damage. For example, using the same word as a neutral prime in an auditory lexical decision task such as “blank” may not be predictive of the target, but it has its own semantic content and may affect the performance of aphasics by dint of its frequent reoccurrence. The use of XXXX in a visual lexical
398
BLUMSTEIN
ET AL.
decision task as a neutral prime, although truly semantically neutral, has the disadvantage of being different from other stimuli and therefore potentially distracting to aphasic patients. In this study, we use nonwords as neutral primes, because they have minimal semantic content, are not repeated, are not in any way predictive of the target, and are similar enough to other stimuli in the experiment to avoid problems with set maintenance inherent in other types of neutral stimuli (see Milberg and Blumstein, 1989). Nonword primes have served as an excellent neutral baseline in a number of previous studies with aphasic patients (cf. Milberg & Blumstein, 1981; Blumstein et al., 1982). EXPERIMENT I Experiment I explored normal and aphasic subjects’ sensitivity to local syntactic dependencies within the same constituent phrase. In particular, we examined subjects’ sensitivity to the grammaticality of modal-verb constructions. We compared reaction-time latencies for a verb target marked for tense or aspect (present, past, progressive) (e.g., going) in three priming conditions: when it is preceded by a syntactically appropriate modal forming a grammatical verb phrase (e.g., is-going); when it is preceded by an inappropriate modal forming a syntactically incorrect verb phrase (e.g., could-going); and when it is preceded by a wrong part of speech such as an adverb, violating strict subcategorization rules and thus not forming a coherent grammatical phrase (e.g., very-going). Performance was compared to a neutral baseline in which the target verb is preceded by a nonword (e.g., plib-going). In addition, we explored whether the morphological endings attached to nonwords affect lexical decision latencies as a function of the appropriateness of the morphological endings (e.g., is-plibbing vs. *could-plibbing). This last condition was included to determine whether a sensitivity to morphological structure would emerge regardless of the lexical status of the word stem. Wright and Garrett (1984) found syntactic priming effects for normals in the context of real words and none in the context of pseudowords marked morphologically. In contrast, Caramazza et al. (1988) showed that lexical decisions for nonwords were affected by the morphological structure of the stimuli. Given the reported differences in sensitivity to the lexical status of words in accessing the lexicon by Broca’s and Wernicke’s aphasics (Milberg et al. 1987), a different pattern of results might emerge in the processing of morphological/syntactic structure as a function of the lexical status of the word stem of the target stimulus. Method Subjects. There were three groups of subjects who participated in this study. These included two groups of normal control subjects and a group of aphasic patients. All of the normal control subjects were right-handed, non-brain-damaged native speakers of English. They
SYNTACTIC
PRIMING
IN APHASIA
399
included a group of 12 college students and a group of 15 veterans of comparable ages to the aphasic subjects. The mean age of the older control subjects was 62 years (SD = 8.56), and they ranged between 46 and 70 years of age. Their average education level was 12.8 years (SD = 2.53). The aphasic patients consisted of 12 male patients, 6 Broca’s and 6 Wernicke’s aphasics from the Aphasia Research Center of the Boston Veterans Administration Hospital. All patients had suffered a single stroke to the left hemisphere. The mean age of the aphasic subjects was 62 years (SD = 6.63), and they ranged in age from 50 to 72 years. Their average education level was comparable to old normal subjects at 13.1 years (SD = 2.09). The aphasia classification of each patient was based on results of the Boston Diagnostic Aphasia Examination (BDAE) (Goodglass & Kaplan, 1968) as well as clinical and neurological examinations. Table 1 presents a summary of the patients’ clinical diagnoses, z scores on the BDAE auditory comprehension subtest, ages at testing and at onset of aphasia, and localization of lesion by CT scan. A number of issues concerning clinical diagnosis are worth raising. First, the diagnosis of patients as Broca’s and Wernicke’s aphasics is made on the basis of their relative performance on a range of speech and language production and comprehension tasks and not on the basis of absolute scores on any individual subtests. Thus, there is some overlap in the auditory comprehension subtest between Broca’s and Wernicke’s aphasics; two Broca’s have negative z scores and three Wernicke’s aphasics, considered mild Wernicke’s, have positive z scores. Second, neurological information was used as part of the aphasia diagnosis. Thus, if a patient were to have clinically a classical Broca’s aphasia with a Wernicke’s area lesion, this patient would not be included in this study. Third, time post-onset ranges significantly among the patients. While this might contribute to increased variance within each group, there is no evidence to date to suggest that such differences contribute to subclasses of patients nor to qualitative distinctions in the patterns of language symptoms described above. Patients with histories of severe alcohol abuse, learning disabilities, severe psychiatric illness, signs of dementia, or head injury with loss of consciousness were not tested. Stimuli. The stimuli consisted of pairs of words and nonwords with the first member of the pair considered the prime and the second member considered the target. Eight types of these prime-target pairs were constructed in order to create four priming conditions for the real word targets (YES responses) and four priming conditions for the nonword targets (NO responses). For the YES response trials, 20 real word targets consisting of a verb form marked for tense or aspect (present, past, progressive) (e.g., going) were preceded by the following four types of primes: an appropriate modal (e.g., is-going) forming a grammatical verb phrase (OK condition); an inappropriate modal (e.g., could-going) forming a syntactically incorrect verb phrase (STAR (*) condition); a wrong part of speech, either an adjective or an adverb (e.g., very-going), violating strict subcategorization rules and thus not forming a coherent verb phrase (WRONG condition); and a nonword (e.g., pru-going) serving as a baseline for comparison of reaction time to the target word (e.g., going) with the other priming conditions (NEUTRAL (N) condition). These same four conditions were constructed for the nonword targets (NO responses) in order to balance the number of YES and NO responses. In addition, the use of the same priming conditions with nonword targets provided a means of determining whether morphological endings attached to nonwords yielded a similar pattern of results to those obtained for real words. Examples of the four priming conditions with nonword targets include: isplibbing (OK condition); could-plibbing (STAR (*) condition); very-plibbing (WRONG condition); pru-plibbing (NEUTRAL condition). Half of the nonword targets consisted of real word stems with incorrect endings (e.g., keeply, wantik) so that subjects would have to listen to the entire target word before responding. Only the nonwords derived from nonword stems were used in the analyses. In summary, the test stimuli consisted of 160 trials: 80 real word targets with 20 stimuli
400
BLUMSTEIN TABLE APHASIC
Diagnosis
ACS
SUBJECTS:
ET AL. 1 EXPERIMENT
Age
Onset
tested
Broca’s
1.04
53
54
Broca’s
.55
50
59
Broca’s Broca’s
-.22 SO
58 58
61 68
Broca’s
-so
63
68
Broca’s/anterior Wernicke’s Wernicke’s
-
67 64 55
72 64 61
Wernicke’s
-.33
57
57
Wernicke’s
- 1.60
62
62
Wernicke’s/conduction
- 1.19
49
50
.53
69
70
Wernicke’s
.71 .30
I
Lesion site
-
Left insula to lateral border of putamen, insula-extreme capsule-claustrum-external capsule; subcortical above Broca’s area, lower motor cortex for face surface and deep (left-handed) Left middle cerebral artery distribution, frontal and parietal involvement Left frontoparietal Posterior frontal and anterior temporal Left subcortical lesion: anterior limb of internal capsule, putamen, globus pallidus extending anterior to frontal horn, patchy in Broca’s area (left-handed) Left anterior, right brainstem Left posterior Left middle cerebral artery territory; posterior temporal and inferior parietal Left posterior temporal lobe with superior extension to supramarginal and angular gyri (surface and deep) and large occipital lesion Temporal in Wernicke’s area, supramarginal and angular gyri; spares temporal isthmus Left deep to angular gyrus cutting off arcuate fasciculus; temporal isthmus; not in Wernicke’s area, posterior periventricular white matter -
y Auditory comprehension z score from the BDAE.
in each of the four priming conditions and 80 nonword targets with 10 stimuli in each of the same four priming conditions as the real words, with the remaining 40 nonword pseudoverb targets created by appending inappropriate endings to real word stems. The test trials were followed by a grammaticality judgement task. This task was given to the old normal subjects and to the aphasic patients. It served as a means of comparing the
SYNTACTIC
PRIMING
IN APHASIA
401
aphasic patients’ performance on a lexical decision task to their performance on a task requiring them to make an overt decision about whether the word pair could appear in a grammatically correct sentence. The performance of the old normal subjects served as a baseline of comparison with the aphasic patients. Stimulus pairs consisted of the real word pairs used in the OK, STAR, and WRONG priming conditions in the lexical decision task. Twenty of these pairs were grammatical and 40 were ungrammatical. Each test stimulus was tape-recorded in a sound-proofed booth on a high quality tape recorder. All stimuli were digitized on a PDPll-34 computer at the Brown University Phonetics Laboratory at a sampling rate of 10 kHz and a lo-bit quantization. The output of the computer was low-pass filtered with a cut-off frequency of 4.8 kHz. The stimulus pairs were presented in a pseudorandom order to maximize the distance between repeated targets. There was a 6-set interval between each stimulus pair and a S-set interval between the members of the pair. Subjects were also provided with four taped practice trials before starting the test. These trials did not appear in the testing session. Apparatus. The apparatus for the experiment consisted of a response board with two 2 x 4-in. keys labeled YES and NO, a voice operated relay and reaction-time clock (Lafayette instruments), a tape recorder (Fisher Stereo AC/DC PH402), and two pairs of sealed headphones. Output of the tape recorder was split so that one channel contained the test stimuli and the other channel contained a brief tone at the onset of each target stimulus. The tone was inaudible to the subject but served to activate the voice operated relay which in turn started the millisecond timer. The subject heard the test stimuli binaurally over the headphones. The examiner monitored the test via the second pair of headphones. Depressing one of the two response keys stopped the timer. Procedure. Subjects were run individually. All but one subject were tested during one session which lasted approximately 45 min. This single remaining subject was tested in two sessions. For the aphasic patients, a session consisted of three tasks which were always administered in the following order: a set induction procedure to train them to perform the lexical decision task, the actual test, and a grammaticality judgement task. (Normal subjects were not given the set induction procedure.) The response board was placed in front of the subject, and the subject was asked to place the fingers of his preferred hand between the two response keys. For some subjects, hand preference was dictated by hemiplegia or hemiparesis. The subject was told that he would hear pairs of words, some of which were real English words and some of which were nonwords. His task was to decide if the second word (the target) was real or not. If it was, he was to press the YES key, and if it was not, he was to press the NO key. Because many of the aphasic subjects suffered from a severe language comprehension deficit, test trials were preceded by a set induction procedure. After the aforementioned instructions, the set induction procedure began. The experimenter presented the subject with several oral exemplars (not used in the actual experiment), first showing the correct responses and then helping the subject to respond, if necessary. This demonstration continued until the subject appeared to comprehend the task and successfully responded to the target. At this point, the subject put on the headphones and received four practice trials. If the subject performed correctly, the test trials began. If he did not, the four practice trials were played again. Once the test trials began, the tape was played continuously unless the subject lost set and responded randomly to a number of consecutive trials. In that case, the tape recorder was stopped, and the set induction procedure was repeated. Subjects were asked to respond as quickly as possible, but not to sacrifice accuracy for speed. No feedback was provided during the test trials. The second task was a grammaticality judgement task. Subjects were asked to indicate whether each pair of words presented could appear together as part of a grammatical English sentence. Subjects were asked to respond YES for grammatical word pairs and NO for
402
BLUMSTEIN
ET AL.
IlOO-
OLD NORMALS
:: I z
iooo-
i g El 2 =
900YOUNG 4 soo-
-1
Z
NORMALS
&k-=-..-
=4
700 ,I WRONG
OK STAR CONDITIONS
NEUTRAL
FIG. 1. Mean lexical decision latencies as a function of syntactic condition for old and young normals in Experiment I.
ungrammatical pairs. As before, the test trials were preceded by a brief description and then another set induction procedure in which the experimenter presented the subjects with several oral exemplars and demonstrated the correct response.
Results Lexical decision: YES responses.The data were analyzed for both mean reaction time (RT) for correct responses and mean number of errors. A series of analyses were conducted for mean latencies of correct lexical decisions to real word targets. The results of the old and young normals were compared to determine whether the patterns of performance were similar for the two control groups. Figure 1 shows the results of this analysis. As the Figure shows, the overall RTs for the old normals were considerably slower than those for the young normals, as expected. However, the patterns of performance for the two groups appear similar. A two-way analysis of variance (Group X Condition) confirmed these results. There was a significant main effect for Group (F(1, 25) = 13.9, p < .OOl) and Condition (F(3, 75) = 10.98, p < .OOOl), and a nonsignificant Group X Condition interaction (F(3, 75) = 1.084, p = .36). Thus, while the two groups differed in their overall RT scores, their patterns of performance were similar. In order to explore the nature of the pattern of the results, the scores of the old and young normals were combined in a single one-way analysis of variance. Post-hoc Duncan tests were conducted to analyze the significance of the main effect obtained for Condition (F(3, 81) = 48.02, p < .OOOl). They revealed the following significant effects: RT latencies
SYNTACTIC
PRIMING
IN APHASIA
403
CONDITIONS
2. Mean lexical decision latencies as a function of syntactic condition for Broca’s and Wernicke’s aphasics in Experiment I. FIG.
for the OK condition were significantly shorter than those for the WRONG condition and the STAR condition; RT latencies in the NEUTRAL baseline condition were significantly slower than those in the OK condition and faster than those in the WRONG condition and the STAR condition. All other comparisons were nonsignificant. Thus, the results for normal subjects revealed syntactic priming in a lexical decision task. In particular, syntactically correct verb phrases were responded to more quickly than either verb phrases containing the wrong modal or syntactically ill-formed verb phrases violating strict subcategorization rules. Since reaction-time latencies in the neutral baseline condition were significantly slower than those in the syntactically correct condition and significantly faster than those in the WRONG and STAR conditions, it may be concluded that the syntactic priming effects have both a facilitory and an inhibitory component. Figure 2 shows the results for the Broca’s and Wernicke’s aphasics. The patterns of responses are clearly different between the two groups. A two-way analysis of variance (Group X Condition) confirmed this finding, showing a significant Group X Condition interaction (F(3, 30) = 4.77, p < .008). All other analyses were nonsignificant. To explore the difference in the patterns of responses for the Broca’s and Wernicke’s aphasics, oneway analyses of variance were conducted for each group separately. Results for the Broca’s aphasics showed a significant effect of Condition (F(3, 15) = 3.52, p < .04). Post-hoc Duncan tests revealed that the WRONG condition was significantly slower than both the STAR and the NEUTRAL conditions. All other comparisons were nonsignificant. Re-
404
BLUMSTJZIN
ET AL.
TABLE 2 MEAN PERCENTAGEOF ERRORSON YES RESWNSESIN EXPERIMENT I WRONG Young normals Old normals Broca’s aphasics Wernicke’s aphasics
5 7 18 22
OK
STAR
4 4 7 18
6 5 20 17
NEUTRAL 4 5 21 19
sults for the Wernicke’s aphasics showed a nonsignificant Condition effect (F(3, 15) = 2.43, p = .ll). Post-hoc Duncan tests revealed that the syntactically OK condition was faster than the NEUTRAL condition. All other comparisons were nonsignificant. Thus, neither Broca’s nor Wernicke’s aphasics showed syntactic facilitation in a lexical decision task. For both groups, no reaction-time differences emerged between syntactically correct and syntactically incorrect verb phrases. Nevertheless, the patterns of results for the two groups were different and suggest potentially different processing components contributing to the obtained effects. In particular, the fact that Broca’s aphasics’ RTs were slower in all conditions compared to the NEUTRAL baseline condition, and significantly so in the WRONG condition, suggests that inhibitory rather than facilitory effects are contributing to the group’s pattern of performance. In contrast, the fact that the Wernicke’s aphasics’ RTs were faster in all conditions compared to the NEUTRAL baseline condition, and significantly so in the OK condition, suggests that facilitory processes rather than inhibitory processes are contributing to the obtained pattern of results. This pattern of facilitation without concurrent inhibition is consistent with the view that these syntactic relationships are processed automatically, without the use of either some syntactically based predictive or other postlexical strategy (de Groot, 1984; Neely, 1976). In addition to the analysis of reaction time for YES responses in the lexical decision task, the data were also analyzed for errors. Table 2 shows the mean percentage of errors on the lexical decision task. As expected, normal subjects made fewer errors than the aphasic patients. Overall performance of the two aphasic groups was quite similar. One-way analyses of variance were conducted on the error data for each group separately to determine if there were any differences in the percentage of errors as a function of the experimental conditions. Results indicated nonsignificant effects for all groups: for young normals, F(3, 33) = 1.18, p = .33; for old normals F(3, 42) = 51, p = .68; for Broca’s aphasics, F(3, 15) = 1.82, p = .19; and for Wernicke’s aphasics, F(3, 15) = .52, p = .68. Grammaticality judgement task. The results of the grammaticality
judge-
SYNTACTIC
LEXICAL
DECISION
LATENCIES
WRONG Young normals Old normals Broca’s aphasics Wernicke’s aphasics
PRIMING
844 1208 1341 1482
405
IN APHASIA
TABLE 3 FOR NO RESPONSES IN EXPERIMENT OK
STAR
859 1231 1426 1411
868 1240 1318 1368
I NEUTRAL 855 1220 1389 1348
ment task indicate that the old normals performed well on this task, producing only 7% errors. These results are significantly above chance (t = 23.04, df = 14, p < .OOOl). The Broca’s aphasics’ performance at 25% errors is above chance (t = 5.3, df = 5, p < .003), although they are not normal in their performance. These results are consistent with earlier findings concerning Broca’s aphasics’ ability to perform grammaticality judgements in sentential material (Linebarger et al., 1983; Baum, 1988). Of particular interest is the fact that while Broca’s aphasics failed to show syntactic priming in a lexical decision task, they nonetheless were able to perform a grammaticality judgement task on the same stimulus items. In contrast, the Wernicke’s aphasics’ performance on the grammaticality judgement task did not differ from chance with a mean of 40% (t = 1.6, df = 5, p = .17). Lexical decision: NO responses. The RT data for NO responses were analyzed to determine if similar syntactic effects emerged for nonwords as were found for real words. Table 3 presents the results for the young and old normals and for the Broca’s and Wernicke’s aphasics. Separate one-way analyses of variance were conducted to determine if there were any significant effects for any of the groups. Results indicated no significant effects for any group: for young normals F(3, 33) = .66, p < .58; for old normals, F(3, 42) = .25, p = .86; for Broca’s aphasics, F(3, 15) = 2.94, p = .07; and for Wernicke’s aphasics, F(3, 15) = .99, p = .42. Thus, nonwords do not exhibit the syntactic effects that were shown for real words. Discussion
Results of Experiment I showed syntactic priming effects for modalverb constructions in a lexical decision task. The observation of facilitation and inhibition in both the young and the old normals suggests that the sensitivity to these local syntactic dependencies invokes both automatic and controlled processing routines for lexical access. This conclusion is based on the assumption that facilitation of syntactically correct verb phrases reflects both automatic and controlled lexical access processes, when in the same experiment inhibition for syntactically incorrect verb phrases is also observed.
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ET AL.
The pattern of performance was different for the two groups of aphasics, and both differed from the normal subjects. The performance of Broca’s aphasics suggests that these patients show no evidence of automatic processing because of the absence of facilitation relative to the baseline condition and the presence of inhibition relative to the baseline condition in the syntactic effects obtained. In contrast, the performance of Wernicke’s aphasics suggests that these patients display a deficit primarily in controlled processing because of the presence of facilitation and the absence of inhibition in the syntactic effects obtained. For each group, the impairment in processing contributed to the failure to obtain differences between the syntactically correct and syntactically incorrect phrases. EXPERIMENT II Experiment I focussed on syntactic priming effects for local syntactic dependencies within the same syntactic phrase, i.e., the verb phrase. In Experiment II, we explored whether similar effects emerged for local syntactic dependencies across phrasal boundaries. To that end, we examined subjects’ sensitivities to the grammaticality of pronoun-verb constructions. Using an analogous design to that of Experiment I, we compared reaction-time latencies for a verb target marked for person and number (e.g., gives) in three priming conditions: when it is preceded by an appropriate subject pronoun forming a grammatical sentence (e.g., he-gives); when it is preceded by an inappropriate pronoun forming a syntactically incorrect sentence (e.g., I-gives); and when it is preceded by a wrong part of speech such as an adjective or an adverb violating strict subcategorization rules and thus not forming a coherent grammatical phrase (e.g., very-gives). Performance was compared to a neutral baseline in which the target verb is preceded by a nonword (e.g., pru-gives). As in Experiment I, we explored whether the morphological endings attached to nonwords affect lexical decision latencies (e.g., he-plibs vs. *they-plibs). Method Subjects.Two groupsof right-handed, non-brain-damaged subjects served as controls. They included 12 college students and 12 veterans of comparable ages to the aphasic subjects. The mean age of the old normals was 60 years old (SD = 9.51), and they ranged in age from 44 to 72 years. The aphasic subjects consisted of a total of 14 male patients, 10 Broca’s, and 4 Wernicke’s aphasics, from the Aphasia Research Center of the Boston VA Medical Center and from the VA Medical Center and Roger Williams Hospital in Providence. The mean age of the aphasic subjects was 60 years (SD = 9.39), and they ranged in age from 43 to 79 years. Table 4 presents a summary of the patients’ clinical diagnoses, z scores on the BDAE auditory comprehension subtest, ages at testing and at onset of aphasia, and localization of lesion (when available) by CT scan. Stimuli. The design of Experiment II was analogous to that of Experiment I. Eight types of prime-target pairs were constructed to create four priming conditions for the real word
SYNTACTIC
PRIMING TABLE
APHASIC
Diagnosis
ACS
SUBJECTS:
IN APHASIA 4
EXPERIMENT
Age
Onset
tested
Broca’s
.63
42
43
Broca’s
.84
49
53
Broca’s
1.04
53
54
42
51
Broca’s
-.15
407
Broca’s
.88
48
58
Broca’s
.I5
56
58
Broca’s
.50
58
69
Broca’s Broca’s
- .22 -SO
58 63
61 68
II Lesion site Left caudate and globus pallidus, anterior internal capsule, to medial temporal cortex and insula, anterior periventricular white matter Left middle cerebral artery distribution, cortical and deep; includes Broca’s area, lower third of motor and sensory strips, anterior limb of internal capsule, lateral putamen and insula-extreme capsuleclaustrum-external capsule Left insula to lateral border of putamen, insula-extreme capsule-claustrum-external capsule; subcortical above Broca’s area, lower motor cortex for face surface and deep (left-handed) Left frontotemporal involving most of Broca’s area extending to subcallosal fasciculus; superior to premotor, motor, sensory cortex; posterior and inferior extension sparing most of Wernicke’s area Inferior-frontal to sylvian fissure deep to ventricles Left hemisphere; in Broca’s area, deep extension to subcallosal fasciculus and insular structures; patchy posterior to temporal isthmus and superior to supramarginal and angular gyri Posterior frontal and anterior temporal Left frontoparietal Left subcortical lesion: anterior limb of internal capsule, putamen, globus pallidus extending anterior to frontal horn, patchy in Broca’s area (left-handed)
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BLUMSTEIN TABLE
Diagnosis
ACS
Wernicke’s
Wernicke’s Wernicke’s Wernicke’s/conduction
4-Continued
Onset
Age tested
60
70
-.33
57
57
53 .66 -1.19
69 77 49
70 79 49
Broca’s
ET AL.
.95
Lesion site Left hemisphere, involving most of Broca’s area with deep extension across to border of left frontal horn; extension to insular structures; superior extension to lower motor cortex for face and lips; additional lesion in less than half of Wernicke’s area Left posterior temporal lobe with superior extension to supramarginal and angular gyri (surface and deep) and large occipital lesion Left internal capsule Left deep to angular gyrus cutting off arcuate fasciculus; temporal isthmus; not in Wernicke’s area, posterior periventricular white matter
a Auditory comprehension z score from the BDAE. targets (YES responses) and four priming conditions for the nonword targets (NO responses). For the YES response trials, 20 real word targets consisting of a verb form marked for person and number (first and third person, singular and plural) (e.g., goes) were preceded by the following four types of primes: an appropriate pronoun (e.g., he-goes) forming a grammatical string (OK condition); an inappropriate pronoun (e.g., they-goes) forming a syntactically incorrect grammatical string (STAR (*) condition); a wrong part of speech, either an adjective or an adverb (e.g., very-goes), violating strict subcategorization rules and thus not forming a correct syntactic structure (WRONG condition); and a nonword (e.g., pru-goes) serving as a baseline for comparison with the other priming conditions (NEUTRAL (N) condition). These same four conditions were constructed for the nonword targets (NO responses). The priming conditions were identical to those used for real words: he plibs (OK condition); they plibs (STAR (*) condition); very plibs (WRONG condition); pru plibs (NEUTRAL condition). Half of the nonsense words consisted of real word stems with incorrect endings. As in Experiment I, the test session was followed by a grammaticality judgement task. The stimulus pairs consisted of the real word pairs used in the OK, STAR, and WRONG priming conditions. Twenty of these pairs were grammatical and 40 were ungrammatical. Apparufus and procedure. The apparatus and procedure were the same as in Experiment I.
Results Lexical decision: YES responses.The data were analyzed for both mean RT for correct responses and mean number of errors. A series of analyses
SYNTACTIC
g F 2 ii
PRIMING
409
IN APHASIA
900SOO-
600 '
YOUNG
I WRONG
1
I
OK STAR CONDITIONS
NORMALS
I NEUTRAL
FIG. 3. Mean lexical decision latencies as a function of syntactic condition for old and young normals in Experiment II.
were conducted on the mean latency data for correct lexical decisions to real word targets. Figure 3 shows the results for the two control groups, the young and old normal subjects. Although the overall RT latencies are clearly different for the two groups, the pattern of results appears similar. A two-way (Group X Condition) analysis of variance confirmed these observations. There was a significant Group effect (F(1,22) = 43.31, p < .OOOl), a significant Condition effect (F(3, 66) = 24.80, p < .OOOl), and a nonsignificant interaction (F(3, 66) = .892, p = .45). In order to explore the nature of the pattern of results, the scores of the old and young normals were combined in a single one-way analysis of variance. Post-hoc Duncan tests were conducted to analyze the significance of the main effect for Condition (F(3, 69) = 24.91, p < .OOl). They revealed the following significant effects: RT latencies for the OK condition were significantly shorter than those for the WRONG condition and the STAR condition; the RT latencies for the NEUTRAL baseline condition were significantly shorter than those for the WRONG and STAR conditions; and, finally, the WRONG condition was significantly faster than the STAR condition. All other comparisons were nonsignificant. Thus, the results for normal subjects revealed syntactic priming effects. That is, syntactically correct pronoun-verb sentences were responded to more quickly than strings that were ungrammatical either because the pronoun and verb were not appropriately matched for person and number or because the phrase violated strict subcategorization rules. In addition, the RT latencies for syntactically incoherent phrases (i.e., those that violated strict subcategorization rules) were significantly slower than RT
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1300
12502 P
1200-
z g p 5 F 2 :
1150-
llOOL --
-=TvERNICKE’S =
