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Processing passive sentences in aphasia: Deficits and strategies
BRAIN
AND
LANGUAGE
30, 93-105 (1987)
Processing Passive Sentences in Aphasia: Deficits and Strategies ANGELA
D. FRIEDERICI AND PATTY A. M. GRAETZ Max-Planck-lnstitur
fiir Psycholinguisrik
Broca’s and Wernicke’s aphasics’ ability to process passive sentences in the absence of semantic cues was investigated in an experiment which varies syntactic complexity and word order. The results indicate that Broca and Wernicke patients use different strategies for sentence comprehension. Wernicke patients use rather general strategies for interpretation, which assign syntactic function according to sequential arrangements of words. Broca’s aphasics, by contrast, base their interpretation on specific structural elements of the sentence’s surface form, without, however, being able to exploit the full syntactic information of these elements. The different strategies are interpreted to reflect differential underlying deficits. 0 1987 Academic Press. Inc.
INTRODUCTION
The understanding of the aphasic language limitations depends, to a great extent, upon assumptions concerning the general relationship between the observable language processes and the architecture of the underlying language system. It seems to be agreed upon that there is a systematic relation between language processors and the functional representation of the language in the brain. Whether, however, observed language behavior of aphasic patients reflects the underlying pathological processes directly, or rather a conglomerate of the basic processes of a deficient but normal language system plus some intervening strategies, is open to debate. In this study the latter view is chosen. Syndrome-specific dysfunctions in the underlying processes are, therefore, taken to have a direct impact for models of normal language use.
An earlier version of this paper was presented at the seventh INS European Conference, Aachen, FRG, 1984. This research has been carried out with support of the Dutch Science Foundation ZWO and the German Max-Planck-Society. Requests for reprints should be sent to Dr. Angela D. Friederici, Max-Planck-Institut fur Psycholinguistik, Wundtlaan, 1, NL-652.5 XD Nijmegen, The Netherlands. 93
0093-934X/87 $3.00 Copyright Q 1987 by Academic Press, Inc. All rights of reproduction in any form reserved.
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Aphasic Comprehension Deficits Most empirical evidence that is taken to support recent views on aphasic deficits derives from studies of language comprehension. After the traditional distinction between Broca’s aphasia as a production deficit and Wernicke’s aphasia as a comprehension deficit was proved to be invalid, a new discussion about the adequate description of the aphasic deficits arose. It had been shown that the syntactic impairment evidenced in the Broca’s aphasic production is mostly paralleled by asyntactic comprehension behavior (Zurif, Caramazza, & Meyerson, 1972;Caramazza & Zurif, 1976). Thus not only Wernicke but also Broca patients were characterized by impaired comprehension. When comparing both patient groups some investigators found similarly impaired performances in the two groups; they took this to reflect the same underlying (syntactic) deficit in Broca’s and Wernicke’s aphasia (e.g., Heeschen, 1980; Parisi & Pizzamiglio, 1970; Shewan & Canter, 1971). Others, however, whose studies yielded clear differences in Broca’s and Wemicke’s comprehension, attributed these to different underlying deficits in the language system (Caramazza & Zurif, 1976; Friederici, 1983; Milberg & Blumstein, 1981; von Stockert & Bader, 1976). Those who argue for a unitary underlying deficit in the two aphasic syndromes usually base their considerations on data from off-line comprehension tasks, e.g., a sentence-picture matching task. Those who take the view of different underlying deficits in Broca’s.and Wernicke’s aphasia can provide evidence from off-line (Caramazza & Zurif, 1976) as well as from on-line measurements (Blumstein, Milberg, & Shirer, 1982; Friederici, 1983; Swinney, Zurif, Rosenberg, & Nicol, 1984). Input Modules and Central Systems Adequate characterizations of the aphasic processing limitations, however, depend upon our understanding of normal language processes. Considering models of normal comprehension, it appears that different tasks measure different stages in the comprehension process. Suppose a processing system in which the incoming information is processed by different linguistic subcomponents which are responsible for lexical, syntactic, semantic, and interpretative processes. It seems to be agreed upon that in normal language understanding these subcomponents operate in an automatic, obligatory fashion. It is still under discussion, however, whether they work in a serial (Forster, 1979), a parallel (Flores d’Arcais, 1982), or an interactive parallel fashion (Marslen-Wilson & Welch, 1978). The model which is used here to describe the comprehension process in the normal adult listener assumes parallel processes in two rather independent parts of the information-processing system, which are connected via a one-way interface. First, there is the language system, which
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consists of a number of autonomous subcomponents (input modules) which process the incoming information automatically. As in the modularity theory (Fodor, 1983) this language system is viewed as being independent from a second, the general cognitive system which in turn, however, takes inputs from the different components of the language system. The general cognitive system (central system) which has access to world knowledge also contains knowledge about the surface characteristics of those languages which are known to the listener. These knowledge sources serve as a basis for a set of interpretative strategies which are used to construct possible interpretations for pieces of information provided by the different components of the language system. In order to allow parallel operations of the language system and the general cognitive system, each of the different language components forwards its information to the general cognitive system as soon as possible. If the sentence representation provided by the language system is complete and can be integrated in the general knowledge, comprehension has taken place. If the language system fails to construct complete sentence representations, the general cognitive system immediately offers possible interpretations based on some interpretative strategies which at least in part are able to compensate for missing linguistic information. These interpretation strategies-used by the normal listener under non-optimal input conditions (e.g., background noise)-may also be applied in case of the aphasic’s failure to construct complete sentence representations. Aphasic Dejicits
and Normal Processes
If one accepts that, by definition, automatic processes are rapid and that strategic processes make more demands on the processing resources and are therefore slower (Shiffrin & Schneider, 1977), it seems viable to assume that on-line measurements tap automatic processes, whereas off-line measurements rather tap a conglomerate of the underlying (impaired) processes plus the application of interpretation strategies. If, furthermore, aphasic deficits are to be located in the underlying processes, their characteristics should be reflected in on-line tasks (Friederici, 1983). In those tasks however, which allow for the use of compensatory strategies-as in off-line tasks-it is likely that different underlying impairments are partly covered by the use of the same strategies. Nonetheless, different strategies should be observable even in off-line tasks, if the particular task taps those very aspects of the language processing system that, in the case of impairment, would necessarily lead to different repair strategies by the general cognitive system. In order to investigate the claim that Broca’s and Wernicke’s aphasias are characterized by different underlying deficits and that these result in the use of different comprehension strategies, an experiment was designed
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that focused on a well-defined linguistic area. Previous findings (Friederici & Kolk, 1983;Kolk & Friederici, 1985)had suggestedthat passive sentences would provide a good testing ground for various comprehension strategies which are based on word order and/or morphological knowledge. Depending upon the disrupted underlying process, Broca’s and Wernicke’s aphasics are expected to use different interpretation strategies. Broca’s aphasics who, according to a recent view, have lost the ability to automatically process the syntactic information given in the closed class elements, i.e., the bound and unbound grammatical morphemes, but are nonetheless able to recognize these items’ form (Bradley, Garrett, & Zurif, 1980) as well as their lexical-semantic specifications (Friederici, 1983, 1985), are expected to use particular closed class forms of the sentence’s surface form as cues for interpretation. Wernicke’s aphasics, who seem to have retained intact automatic lower level semantic and syntactic processes, but not those which are responsible for the integration of these different types of information at a higher level (Milberg & Blumstein, 1981; Friederici, 1983), are assumed to use compensatory strategies which are-at least in part-different from those used by Broca’s aphasics. METHOD
Material The Dutch language, which, in contrast to English, allows various word order configurations, provides the possibility to construct passive sentences of different word order. The experiment used semantically reversible sentences. Passive sentences varied with respect to the order of the syntactic subject and object noun: half of the sentences were agent-first constructions, half were patient-first constructions. They also varied at three degrees of syntactic complexity (complexity here refers to the sentence’s surface form as well as to the sentence’s modus): (1) simple passive, (2) a question + passive construction (implicitly directive), (3) a construction with an explicit imperative which in addition causes a syntactic relative. Each condition was represented by 20 items. See Table 1 for examples. Eighteen active sentence/question/imperative + question) were used as distracters.
Procedure The experiment used a sentence-picture matching task. Sentences were presented visually in order to minimize effects of auditory memory. Subjects were asked to read the sentence aloud. Here the experimenter’s intention was to make sure that the patient processed each word at least at a peripheral level. In case of incorrect reading (e.g., word omission or substitution) the sentence was repeated back to the patient in its correct form. The subject was requested to indicate his comprehension by choosing the correct picture out of an array of three (the correct picture, a syntactic distractor in which agent and patient were reversed, a lexical distractor in which either the depicted agent, the patient, or the action did not correspond to the sentence). There was no time limit in this task. The stimulus material was presented in two separate sessions, each lasting about 20 min.
Subjects Sixteen patients who had suffered from a cerebrovascular lesion of the dominant left hemisphere participated in this study. They were all right-handed and native speakers of
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TABLE I EXAMPLES OF TEST ITEMS
Simple passive Example: The boy is being kissed by the girl Patient first De jongen wordt door het meisje gekust. kissed by the girl The boy is-being Agent first Door het meisje wordt de jongen gekust. the boy kissed By the girl is-being Passive + question Example: In which picture is the boy being kissed by the girl? Patient first Op welk plaatje wordt de jongen door het meisje gekust? In which picture kissed is-being the boy by the girl Agent first Op welk plaatje wordt door her meisje de jongen gekust? In which picture the boy kissed is-being by the girl Passive + question + imperative Example: Show me where the boy is being kissed by the girl Patient first Laat u mij zien, waar de jongen door het meisje geslagen wordt. Let you me see, kissed is-being the girl where the boy by Agent first Laat u mij zien, waar door het meisje de jongen geslagen wordt. Let you me see, where by the girl the boy kissed is-being Dutch. They were classified according to their scores on the Dutch version of the Aachen Aphasia Test, which is constructed by analogy to the German version of the AAT (Huber, Poeck, Weniger, & Wilmes, 1983), and the clinical examination of neurologists. A group of eight patients with anterior lesions were classified as Broca’s aphasics. They showed the characteristic nonfluent speech with poor syntactic structure. Their auditory as well as reading comprehension was not, or only mildly, disturbed and in one case moderately disturbed. Seven of eight patients with posterior lesions were classified as Wenicke’s aphasics and the remaining one as anemic. The spontaneous speech of both the Wemicke patients and the anemic patient was fluent. The Wernicke patients showed in addition paragrammatic speech with phonemic or semantic paraphasias. Their auditory and reading comprehension was good to moderate and in only one case severely disturbed. We refer to these groups as the Broca’s and the Wernicke’s aphasics, respectively, for reasons of abbreviation. For individual patient data see Table 2.
m f m m m m m m
B. so.
62 12 71 64 62 65 71 55
43 62 65 63 66 66 54 57
Age
41 39 35 31 22 12 10 10
33 28 19 14 13 8 6 4
Token Test
Wemicke Wemicke Wernicke Wernicke Wernicke Wernicke Wernicke Anemic
Broca Broca Broca Broca Broca Broca Broca Broca Severe Moderate Mild Moderate Mild Mild No No
No Moderate Mild No Mild Mild No No
Overall comprehension disturbance”
HISTORY
22 23 21 19 22 24 30 25
26 17 21 28 21 30 23 25
Sentence comprehension auditory
6 14 22 21 26 25 26 25
28 15 20 26 25 23 27 23
Sentence comprehension reading
a Overall comprehension scores are based on four subtests in each of which 30 points can be reached: (1) word comprehension auditory, (2) sentence comprehension auditory, (3) word comprehension reading, (4) sentence comprehension reading.
H. D. V.W. J. R. v.K. V.I. V.O.
d.W. v.R. R. N. SW.
VS.
Sex
SU
PATIENT
TABLE 2 Classification according AAT
INDIVIDUAL
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PASSIVE SENTENCES IN APHASIA TABLE 3 MEAN PERCENTAGEERRORSFOR APHAW GROUPS
Complexity
Word order Syntactic errors Broca Wernicke
Passive + question + imperative
Passive + question
Simple passive Patient first
Agent first
Patient first
Agent first
Patient first
Agent first
11.9 23.7
8.1 11.2
11.9 21.3
10.0 13.1
12.5 23.1
11.2 9.4
1.3 3.1
1.9 3.1
0.6 3.8
1.3 1.9
0.0 4.4
1.3 3.8
Lexical errors Broca Wernicke ___-
RESULTS
Active sentences (distractor items) were processed correctly in nearly all instances. Percentage means of incorrect choices for active sentences was 2.0% for Broca’s aphasics and 3.75% for Wemicke’s aphasics. Further analysis thus focused on responses to passives sentences (test items) only. Percentage means of incorrect choices (syntactic distractor and lexical distractor) for the two aphasic groups are given in Table 3. The number of syntactic errors for the different conditions is also displayed in Fig. 1. Individual patient data are listed in Tables 4 and 5. An analysis of variance with the factors Aphasic Group x Complexity x Word Order x Error Type was computed. The main effect of Aphasic
o\
\
BROCA’S. WERNICKE’S 0
0, \
O\ \
\
\ \
\
‘\ \
\
\
\
\
FIG. 1. Aphasics: Broca’s (N = 8) & Wernicke’s (N = 8).
\
\
FRIEDERICI
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TABLE 4 INDIVIDUAL
PATIENT
DATA:
BROCA’S APHASICS
I Complexity Simple passive
Passive + question + imperative
Passive + question
Patient first
Agent first
Patient first
Agent first
Patient first
Agent first
Syntactic errors B. so. V.S. d.W. r.R. R. N. SW.
5 5 1 4 1 1 1 1
1 3 0 1 1 3 3 2
7 7 0 2 1 0 3 0
2 4 1 3 1 3 1 5
9 5 0 2 0 0 1 2
2 5 1 1 0 2 2 3
Lexical errors B. so. vs. d.W. v.R. R. N. SW.
0 1 0 0 0 0 1 0
0 1 0 1 0 0 0 0
0 0 0 0 0 0 0 0
0 2 0 0 0 0 0 0
0 1 0 0 0 0 0 0
0 1 1 0 0 0 1 0
Word order
Group was significant (F(1, 14) = 5.5, p < .05), with Broca’s aphasics showing a better overall performance than Wernicke’s aphasics. The Error Type main effect was also significant (F(1, 14) = 56.87, p < .Ol), reflecting the finding that more syntactic than lexical errors were made. No other main effect was significant. The Aphasic Group x Word Order interactions show that Wernicke patients are more likely to make incorrect choices in patient-first sentences, whereas Broca patients demonstrate no difference in performance for the different word order types. The interaction was marginally significant (F(1, 14) = 4.43, p < .06). The significant Error Type x Word Order interaction (F(1, 14) = 6.33, p < .05) indicates that more syntactic errors are made in patient-first sentences than in agent-first sentences, whereas no such difference is present for the lexical errors. DISCUSSION
The different patterns of performance for the two aphasic groups are in agreement with the view that the comprehension limitations in Wemicke’s aphasia and Broca’s aphasia are due to different underlying deficits in
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PASSIVE SENTENCES IN APHASIA TABLE 5 INDIVIDUAL
PATIENT
DATA:
WERNICKE’S
APHASICS
Complexity Simple passive Word order Syntactic errors H. D. V.W. J. Ii. v.K. V.I. V.O. Lexical errors H. D. V.W. J. R. v.K. V.I.
V.O.
Patient first
Agent first
Passive + question + imperative
Passive + question Patient first
Agent first
Patient first
Agent first
2 4 2 5 6 5 6 6
2 2 I 2 0 3 3 3
3 4 2 3 7 4 5 6
3 4 I 4 I 2 2 3
4 2 I 2 0 0 0 0
I 4 0 0 0 0 I 0
2 I 0 2 0 0 I 0
I 0 I 2 0 0 0 0
the language processing system. Since the task chosen in the experiment was off-line in nature these findings do not necessarily force a differential deficit view. In combination, however, with recent on-line results (Friederici, 1983, 1985, Swinney et al., 1986), this conclusion seems more than viable. The findings for the Wernicke’s aphasics indicate that these patients follow a very general strategy for sentence interpretation, which may even be based on cognitive principles. Wernicke’s aphasics show a clear tendency to assign the first noun in a sentence as the agent, independent of the actual word order and the syntactic complexity. These patients do not seem to base their interpretation on cues given by the morphological passive markers, but rather they rely on strategies which may be provided by the central cognitive system. Broca’s aphasics, by contrast, show equal performance for all passive constructions independent of word order and syntactic complexity. Their comprehension performance for passive sentences was remarkably good, suggesting that these patients follow an interpretation principle which requires the recognition of particular closed class elements in the sentence
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surface form. The only structural configuration that remains constant in all six types of passive sentences is the presence of the passive morphology: the auxiliary, the past participle, and the “by-phrase” in which the noun is marked for agenthood by a preposition. Even though it is obvious that agrammatic aphasics are not able to fully use the structural information given by the passive morphology for unambiguous assignment-their performance is not perfect-these patients seem to use a comprehension strategy which considers these elements to mark structure. The presented findings are in variance with the proposal put forward by Caplan (1983) that performance of agrammatic aphasics (English speaking) could be explained by the possible use of conflicting principles, each relying on different cues for interpretation-such as animacy, word order, and local structural cues. When two principles are in conflict, unambigous assignment of thematic roles is not possible. This approach predicts that in the case of reversible passive sentences, where two principles (word order and local structural cues) are in conflict, patients should perform at random-a pattern of performance which was reported for a case of an English-speaking agrammatic patient by Caplan and Futter (1986). The notion of conflicting information has also been used by Grodzinsky (1984) although at a different level of description. He characterizes agrammatism within a particular linguistic theory (Chomsky, 1981), which defines different levels of representation. At one level (s-structure representation) all members of major categories are lexically specified, whereas the restthat is, the closed class items with the exception of some prepositions (which satisfy a particular structural condition )-are specified only by features. What is specified at this level with respect to an English passive sentence are the major category items as well as the preposition by which marks agenthood. It is to this level of representation that agrammatic patients have access. Although Grodzinsky (1984) calls for consistency within the level of description for accounts of aphasic deficits, he leaves the level of linguistic description when he claims that Broca’s aphasics should perform at random with passive sentences in English due to two qualitatively different types of conflicting information: at the level of linguistic representation the patient is able to recognize the by as the sign of agenthood; within the domain of strategic operations, however, a default principle requires that the noun in subject position should be assigned as the agent. Grodzinsky cites the results obtained by Caplan and Futter (1986) as supporting his view. Unfortunately, however, this study does not provide the critical test Grodzinsky would need to show that the default principle operates in the absence of a passive by-phrase. His view would predict agentless passives to be interpreted 100%incorrectly by agrammatics.
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The nonrandom performance for the Dutch-speaking agrammatic Broca’s aphasics observed in the present study, however, can only be explained within either of these approaches if certain interpretation principles are language-specific. Given that Dutch has less strict word order constraints than English, possible conflicts between knowledge about local structural markers such as the passive morphology and some global word order strategy (e.g., agent-first) are less likely to occur in Dutch than in English. One explanation for the findings in both languages could be formulated as follows: agrammatic aphasics are able to recognize those structural elements which play the role of a thematic role assigner such as agent, theme, goal, and others (Rizzi, 1985). However, since access to the structural information of closed class elements is not complete, the language system is not able to construct an adequate structural sentence representation. The incomplete linguistic representation is forwarded to the general cognitive system where interpretation strategies, which are based upon general world knowledge, compensate for missing structural information. Agrammatics’ off-line comprehension performance presented here seems to reflect a specific deficit of the underlying structural processes rather than the application of compensatory strategies. The underlying deficit of agrammatic Broca’s aphasics can be located in the structural domain: the deficit, however, is less general than previously assumed. Agrammatic Broca’s aphasics are able to recognize those closed class elements which assign thematic roles. They are, however, unable to access all features of the structural information given by these elements. Results from this study-in combination with findings from some recent on-line studies (Friederici, 1983: Swinney et al., 1984)-provide evidence for the view that the underlying deficits of Broca’s and Wemicke’s aphasia are of a different type. Pursuing the distinction between underlying language processes and interpretation strategies in a model of language comprehension, the similarities in Broca’s and Wemicke’s aphasics’ comprehension in some off-line tasks are not attributed to a unitary deficit but rather to the use of a number of cognitively based strategies which may sometimes lead to the identical interpretations of given sentences. At present, the deficit underlying the performance of Wemicke’s aphasics remains unspecified. The conclusion that can be drawn from the available on-line and off-line data suggests that Wernicke patients have retained the ability to automatically process elements of either grammatical class in the initial processing phase. Their comprehension difficulties arise at a level where integration of semantic and syntactic information takes place. Interpretation seems to be guided by some general strategies which are part of the cognitive system and which, in the absence of semantic or pragmatic cues, use global structural information about the sequential arrangement of words to assign thematic roles.
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Broca’s aphasics’ processing may be specified as being due to limitations in accessing the full structural information of closed class elements. They are left with the ability to recognize these items’ forms, their lexicalsemantic specifications, their thematic role assigning function, without being able to exploit all aspects of the information given by these items. The observed structural deficit, however, is more restricted than previous views assumed. Future research is clearly necessary to specify these restrictions and their constraints for models of normal language use. REFERENCES Bemdt, R. S., & Caramazza, A. 1980. A redefinition of the syndrome of Broca’s aphasia: Implications for a neuropsychological model of language. Applied Psycholinguistics, 1, 225-278.
Blumstein, S. E., Milberg, W., & Shirer, R. 1982.Semantic processing in aphasia: Evidence from an auditory lexical decision task. Brain and Language, 17, 301-315. Bradley, D. C., Garrett, M. F., & Zurif, E. B. 1980. Syntactic deficits in Broca’s aphasia. In D. Caplan (Ed.), Biological studies of mental processes. Cambridge, Mass.: MIT Press. Caplan, D. 1983.A note on the “word order problem” in agrammatism. Brain and Language, 20, 155-165.
Caplan, D., & Futter, C. 1986. Assignment of thematic roles to nouns in sentence comprehension by an agrammatic patient. Bruin and Language, 27, 117-134. Caramazza, A., & Zurif, E. B. 1976. Dissociation of algorithmic and heuristic processes in language comprehension. Bruin and Language, 3, 572-582. Chomsky, N. 1981. Lectures on government and binding. The Pisa lectures. Dordrecht: Foris Publications. Flores d’Arcais, G. B. 1982. Automatic syntactic computation and the use of semantic information during sentence comprehension. Psychological Research, 44, 231-242. Fodor, J. A. 1983. The modularity of mind. Cambridge, Mass.: MIT Press. Forster, K. I. 1979. Levels of processing and the structure of the language processor. In R. Wales & E. C. T. Walker (Eds.), New approaches to language mechanisms. Amsterdam: North-Holland. Friederici, A. D. 1983. Aphasic’s perception of words in sentential context: Some realtime processing evidence. Neuropsychologia, 21, 351-358. Friederici, A. D. 1985. Levels of processing and vocabulary type: Evidence from normal and agrammatic listeners. Cognition, 19, 133-166. Friederici, A. D., & Kolk, H. H. 1983. Sensitivity to word order and case in agrammatism. Paper presented to the First European Workshop on Cognitive Neuropsychology, Bressanone, Italy. Grodzinsky, Y. 1984. The syntactic characterization of agrammatism. Cognition, 16, 99120.
Grodzinsky, Y. 1986. Language deficits and the theory of syntax, Brain and Language, 22, 135-159.
Huber, W., Poeck, K., Weniger, D., & Wilmes, K. 1983.Aachlner Aphasic Test, Gottingen: Hogrefe . Kolk, H. H. J., & Friederici, A. D. 1985. Strategy and impairment in sentence understanding by Broca’s and Wernicke’s aphasics, Cortex, 21, 47-67. Heeschen, C. 1980. Strategies of decoding actor-object-relations by aphasic patients. Cortex, 16, 5-19.
Heeschen, C. 1985. Agrammatism and paragrammatism: A fictitious opposition. In M.-L. Kean (Ed.), Agrammatism. New York: Academic Press.
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Marslen-Wilson, W. D., & Welch, A. 1978. Processing interactions and lexical access during word recognition in continuous speech. Cognitive Psychology, 10, 29-63. Meyer, D. M., Schvaneveldt, R. W. & Ruddy, M. G. 1971. Loci of contextual effects on word recognition. In P. A. M. Rabbitt & S. Dornic (Eds.), Attenfion undperformance (Vol. 5). New York: Academic press. Milberg, W., & Blumstein, S. E. 1981. Lexical decision and aphasia: Evidence for semantic processing. Brain and Lnnguage, 14, 371-385. Parisi, D., & Pizzamiglio, L. 1970. Syntactic comprehension in aphasia. Cortex, 6, 204215. Rizzi, L. 1985. Two notes on the linguistic interpretation of Broca’s aphasia. In M.-L. Kean (Ed.) Agrammarism. New York: Academic Press. Schwartz, M. F., Saffran, E. M., & Marin, 0. S. M. 1980. The word order problem in agrammatism. 1. Comprehension. Brain and Language. 10, 249-262. Shewan, C. M., & Canter, G. J. 1971. Effects on vocabulary, syntax and sentence length on auditory comprehension in aphasic patients. Correx, 7, 209-226. Shiffrin, R. M., & Schneider, W. 1977. Controlled and automatic human information processing II. Perceptual learning, automatic attending and a general theory. Psychological Review,
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Swinney, D., Zurif, E., Rosenberg, B., & Nicol, J. 1984. Modularity and information access in the lexicon: Evidence from aphasia. Paper presented at the Academy of Aphasia. Los Angeles. Brain and Language. submitted. von Stockert, R. T., & Bader, L. 1976. Some relations of grammar and lexicon in aphasia. Cortex,
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AND
LANGUAGE
30, 93-105 (1987)
Processing Passive Sentences in Aphasia: Deficits and Strategies ANGELA
D. FRIEDERICI AND PATTY A. M. GRAETZ Max-Planck-lnstitur
fiir Psycholinguisrik
Broca’s and Wernicke’s aphasics’ ability to process passive sentences in the absence of semantic cues was investigated in an experiment which varies syntactic complexity and word order. The results indicate that Broca and Wernicke patients use different strategies for sentence comprehension. Wernicke patients use rather general strategies for interpretation, which assign syntactic function according to sequential arrangements of words. Broca’s aphasics, by contrast, base their interpretation on specific structural elements of the sentence’s surface form, without, however, being able to exploit the full syntactic information of these elements. The different strategies are interpreted to reflect differential underlying deficits. 0 1987 Academic Press. Inc.
INTRODUCTION
The understanding of the aphasic language limitations depends, to a great extent, upon assumptions concerning the general relationship between the observable language processes and the architecture of the underlying language system. It seems to be agreed upon that there is a systematic relation between language processors and the functional representation of the language in the brain. Whether, however, observed language behavior of aphasic patients reflects the underlying pathological processes directly, or rather a conglomerate of the basic processes of a deficient but normal language system plus some intervening strategies, is open to debate. In this study the latter view is chosen. Syndrome-specific dysfunctions in the underlying processes are, therefore, taken to have a direct impact for models of normal language use.
An earlier version of this paper was presented at the seventh INS European Conference, Aachen, FRG, 1984. This research has been carried out with support of the Dutch Science Foundation ZWO and the German Max-Planck-Society. Requests for reprints should be sent to Dr. Angela D. Friederici, Max-Planck-Institut fur Psycholinguistik, Wundtlaan, 1, NL-652.5 XD Nijmegen, The Netherlands. 93
0093-934X/87 $3.00 Copyright Q 1987 by Academic Press, Inc. All rights of reproduction in any form reserved.
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Aphasic Comprehension Deficits Most empirical evidence that is taken to support recent views on aphasic deficits derives from studies of language comprehension. After the traditional distinction between Broca’s aphasia as a production deficit and Wernicke’s aphasia as a comprehension deficit was proved to be invalid, a new discussion about the adequate description of the aphasic deficits arose. It had been shown that the syntactic impairment evidenced in the Broca’s aphasic production is mostly paralleled by asyntactic comprehension behavior (Zurif, Caramazza, & Meyerson, 1972;Caramazza & Zurif, 1976). Thus not only Wernicke but also Broca patients were characterized by impaired comprehension. When comparing both patient groups some investigators found similarly impaired performances in the two groups; they took this to reflect the same underlying (syntactic) deficit in Broca’s and Wernicke’s aphasia (e.g., Heeschen, 1980; Parisi & Pizzamiglio, 1970; Shewan & Canter, 1971). Others, however, whose studies yielded clear differences in Broca’s and Wemicke’s comprehension, attributed these to different underlying deficits in the language system (Caramazza & Zurif, 1976; Friederici, 1983; Milberg & Blumstein, 1981; von Stockert & Bader, 1976). Those who argue for a unitary underlying deficit in the two aphasic syndromes usually base their considerations on data from off-line comprehension tasks, e.g., a sentence-picture matching task. Those who take the view of different underlying deficits in Broca’s.and Wernicke’s aphasia can provide evidence from off-line (Caramazza & Zurif, 1976) as well as from on-line measurements (Blumstein, Milberg, & Shirer, 1982; Friederici, 1983; Swinney, Zurif, Rosenberg, & Nicol, 1984). Input Modules and Central Systems Adequate characterizations of the aphasic processing limitations, however, depend upon our understanding of normal language processes. Considering models of normal comprehension, it appears that different tasks measure different stages in the comprehension process. Suppose a processing system in which the incoming information is processed by different linguistic subcomponents which are responsible for lexical, syntactic, semantic, and interpretative processes. It seems to be agreed upon that in normal language understanding these subcomponents operate in an automatic, obligatory fashion. It is still under discussion, however, whether they work in a serial (Forster, 1979), a parallel (Flores d’Arcais, 1982), or an interactive parallel fashion (Marslen-Wilson & Welch, 1978). The model which is used here to describe the comprehension process in the normal adult listener assumes parallel processes in two rather independent parts of the information-processing system, which are connected via a one-way interface. First, there is the language system, which
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consists of a number of autonomous subcomponents (input modules) which process the incoming information automatically. As in the modularity theory (Fodor, 1983) this language system is viewed as being independent from a second, the general cognitive system which in turn, however, takes inputs from the different components of the language system. The general cognitive system (central system) which has access to world knowledge also contains knowledge about the surface characteristics of those languages which are known to the listener. These knowledge sources serve as a basis for a set of interpretative strategies which are used to construct possible interpretations for pieces of information provided by the different components of the language system. In order to allow parallel operations of the language system and the general cognitive system, each of the different language components forwards its information to the general cognitive system as soon as possible. If the sentence representation provided by the language system is complete and can be integrated in the general knowledge, comprehension has taken place. If the language system fails to construct complete sentence representations, the general cognitive system immediately offers possible interpretations based on some interpretative strategies which at least in part are able to compensate for missing linguistic information. These interpretation strategies-used by the normal listener under non-optimal input conditions (e.g., background noise)-may also be applied in case of the aphasic’s failure to construct complete sentence representations. Aphasic Dejicits
and Normal Processes
If one accepts that, by definition, automatic processes are rapid and that strategic processes make more demands on the processing resources and are therefore slower (Shiffrin & Schneider, 1977), it seems viable to assume that on-line measurements tap automatic processes, whereas off-line measurements rather tap a conglomerate of the underlying (impaired) processes plus the application of interpretation strategies. If, furthermore, aphasic deficits are to be located in the underlying processes, their characteristics should be reflected in on-line tasks (Friederici, 1983). In those tasks however, which allow for the use of compensatory strategies-as in off-line tasks-it is likely that different underlying impairments are partly covered by the use of the same strategies. Nonetheless, different strategies should be observable even in off-line tasks, if the particular task taps those very aspects of the language processing system that, in the case of impairment, would necessarily lead to different repair strategies by the general cognitive system. In order to investigate the claim that Broca’s and Wernicke’s aphasias are characterized by different underlying deficits and that these result in the use of different comprehension strategies, an experiment was designed
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that focused on a well-defined linguistic area. Previous findings (Friederici & Kolk, 1983;Kolk & Friederici, 1985)had suggestedthat passive sentences would provide a good testing ground for various comprehension strategies which are based on word order and/or morphological knowledge. Depending upon the disrupted underlying process, Broca’s and Wernicke’s aphasics are expected to use different interpretation strategies. Broca’s aphasics who, according to a recent view, have lost the ability to automatically process the syntactic information given in the closed class elements, i.e., the bound and unbound grammatical morphemes, but are nonetheless able to recognize these items’ form (Bradley, Garrett, & Zurif, 1980) as well as their lexical-semantic specifications (Friederici, 1983, 1985), are expected to use particular closed class forms of the sentence’s surface form as cues for interpretation. Wernicke’s aphasics, who seem to have retained intact automatic lower level semantic and syntactic processes, but not those which are responsible for the integration of these different types of information at a higher level (Milberg & Blumstein, 1981; Friederici, 1983), are assumed to use compensatory strategies which are-at least in part-different from those used by Broca’s aphasics. METHOD
Material The Dutch language, which, in contrast to English, allows various word order configurations, provides the possibility to construct passive sentences of different word order. The experiment used semantically reversible sentences. Passive sentences varied with respect to the order of the syntactic subject and object noun: half of the sentences were agent-first constructions, half were patient-first constructions. They also varied at three degrees of syntactic complexity (complexity here refers to the sentence’s surface form as well as to the sentence’s modus): (1) simple passive, (2) a question + passive construction (implicitly directive), (3) a construction with an explicit imperative which in addition causes a syntactic relative. Each condition was represented by 20 items. See Table 1 for examples. Eighteen active sentence/question/imperative + question) were used as distracters.
Procedure The experiment used a sentence-picture matching task. Sentences were presented visually in order to minimize effects of auditory memory. Subjects were asked to read the sentence aloud. Here the experimenter’s intention was to make sure that the patient processed each word at least at a peripheral level. In case of incorrect reading (e.g., word omission or substitution) the sentence was repeated back to the patient in its correct form. The subject was requested to indicate his comprehension by choosing the correct picture out of an array of three (the correct picture, a syntactic distractor in which agent and patient were reversed, a lexical distractor in which either the depicted agent, the patient, or the action did not correspond to the sentence). There was no time limit in this task. The stimulus material was presented in two separate sessions, each lasting about 20 min.
Subjects Sixteen patients who had suffered from a cerebrovascular lesion of the dominant left hemisphere participated in this study. They were all right-handed and native speakers of
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TABLE I EXAMPLES OF TEST ITEMS
Simple passive Example: The boy is being kissed by the girl Patient first De jongen wordt door het meisje gekust. kissed by the girl The boy is-being Agent first Door het meisje wordt de jongen gekust. the boy kissed By the girl is-being Passive + question Example: In which picture is the boy being kissed by the girl? Patient first Op welk plaatje wordt de jongen door het meisje gekust? In which picture kissed is-being the boy by the girl Agent first Op welk plaatje wordt door her meisje de jongen gekust? In which picture the boy kissed is-being by the girl Passive + question + imperative Example: Show me where the boy is being kissed by the girl Patient first Laat u mij zien, waar de jongen door het meisje geslagen wordt. Let you me see, kissed is-being the girl where the boy by Agent first Laat u mij zien, waar door het meisje de jongen geslagen wordt. Let you me see, where by the girl the boy kissed is-being Dutch. They were classified according to their scores on the Dutch version of the Aachen Aphasia Test, which is constructed by analogy to the German version of the AAT (Huber, Poeck, Weniger, & Wilmes, 1983), and the clinical examination of neurologists. A group of eight patients with anterior lesions were classified as Broca’s aphasics. They showed the characteristic nonfluent speech with poor syntactic structure. Their auditory as well as reading comprehension was not, or only mildly, disturbed and in one case moderately disturbed. Seven of eight patients with posterior lesions were classified as Wenicke’s aphasics and the remaining one as anemic. The spontaneous speech of both the Wemicke patients and the anemic patient was fluent. The Wernicke patients showed in addition paragrammatic speech with phonemic or semantic paraphasias. Their auditory and reading comprehension was good to moderate and in only one case severely disturbed. We refer to these groups as the Broca’s and the Wernicke’s aphasics, respectively, for reasons of abbreviation. For individual patient data see Table 2.
m f m m m m m m
B. so.
62 12 71 64 62 65 71 55
43 62 65 63 66 66 54 57
Age
41 39 35 31 22 12 10 10
33 28 19 14 13 8 6 4
Token Test
Wemicke Wemicke Wernicke Wernicke Wernicke Wernicke Wernicke Anemic
Broca Broca Broca Broca Broca Broca Broca Broca Severe Moderate Mild Moderate Mild Mild No No
No Moderate Mild No Mild Mild No No
Overall comprehension disturbance”
HISTORY
22 23 21 19 22 24 30 25
26 17 21 28 21 30 23 25
Sentence comprehension auditory
6 14 22 21 26 25 26 25
28 15 20 26 25 23 27 23
Sentence comprehension reading
a Overall comprehension scores are based on four subtests in each of which 30 points can be reached: (1) word comprehension auditory, (2) sentence comprehension auditory, (3) word comprehension reading, (4) sentence comprehension reading.
H. D. V.W. J. R. v.K. V.I. V.O.
d.W. v.R. R. N. SW.
VS.
Sex
SU
PATIENT
TABLE 2 Classification according AAT
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PASSIVE SENTENCES IN APHASIA TABLE 3 MEAN PERCENTAGEERRORSFOR APHAW GROUPS
Complexity
Word order Syntactic errors Broca Wernicke
Passive + question + imperative
Passive + question
Simple passive Patient first
Agent first
Patient first
Agent first
Patient first
Agent first
11.9 23.7
8.1 11.2
11.9 21.3
10.0 13.1
12.5 23.1
11.2 9.4
1.3 3.1
1.9 3.1
0.6 3.8
1.3 1.9
0.0 4.4
1.3 3.8
Lexical errors Broca Wernicke ___-
RESULTS
Active sentences (distractor items) were processed correctly in nearly all instances. Percentage means of incorrect choices for active sentences was 2.0% for Broca’s aphasics and 3.75% for Wemicke’s aphasics. Further analysis thus focused on responses to passives sentences (test items) only. Percentage means of incorrect choices (syntactic distractor and lexical distractor) for the two aphasic groups are given in Table 3. The number of syntactic errors for the different conditions is also displayed in Fig. 1. Individual patient data are listed in Tables 4 and 5. An analysis of variance with the factors Aphasic Group x Complexity x Word Order x Error Type was computed. The main effect of Aphasic
o\
\
BROCA’S. WERNICKE’S 0
0, \
O\ \
\
\ \
\
‘\ \
\
\
\
\
FIG. 1. Aphasics: Broca’s (N = 8) & Wernicke’s (N = 8).
\
\
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TABLE 4 INDIVIDUAL
PATIENT
DATA:
BROCA’S APHASICS
I Complexity Simple passive
Passive + question + imperative
Passive + question
Patient first
Agent first
Patient first
Agent first
Patient first
Agent first
Syntactic errors B. so. V.S. d.W. r.R. R. N. SW.
5 5 1 4 1 1 1 1
1 3 0 1 1 3 3 2
7 7 0 2 1 0 3 0
2 4 1 3 1 3 1 5
9 5 0 2 0 0 1 2
2 5 1 1 0 2 2 3
Lexical errors B. so. vs. d.W. v.R. R. N. SW.
0 1 0 0 0 0 1 0
0 1 0 1 0 0 0 0
0 0 0 0 0 0 0 0
0 2 0 0 0 0 0 0
0 1 0 0 0 0 0 0
0 1 1 0 0 0 1 0
Word order
Group was significant (F(1, 14) = 5.5, p < .05), with Broca’s aphasics showing a better overall performance than Wernicke’s aphasics. The Error Type main effect was also significant (F(1, 14) = 56.87, p < .Ol), reflecting the finding that more syntactic than lexical errors were made. No other main effect was significant. The Aphasic Group x Word Order interactions show that Wernicke patients are more likely to make incorrect choices in patient-first sentences, whereas Broca patients demonstrate no difference in performance for the different word order types. The interaction was marginally significant (F(1, 14) = 4.43, p < .06). The significant Error Type x Word Order interaction (F(1, 14) = 6.33, p < .05) indicates that more syntactic errors are made in patient-first sentences than in agent-first sentences, whereas no such difference is present for the lexical errors. DISCUSSION
The different patterns of performance for the two aphasic groups are in agreement with the view that the comprehension limitations in Wemicke’s aphasia and Broca’s aphasia are due to different underlying deficits in
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PASSIVE SENTENCES IN APHASIA TABLE 5 INDIVIDUAL
PATIENT
DATA:
WERNICKE’S
APHASICS
Complexity Simple passive Word order Syntactic errors H. D. V.W. J. Ii. v.K. V.I. V.O. Lexical errors H. D. V.W. J. R. v.K. V.I.
V.O.
Patient first
Agent first
Passive + question + imperative
Passive + question Patient first
Agent first
Patient first
Agent first
2 4 2 5 6 5 6 6
2 2 I 2 0 3 3 3
3 4 2 3 7 4 5 6
3 4 I 4 I 2 2 3
4 2 I 2 0 0 0 0
I 4 0 0 0 0 I 0
2 I 0 2 0 0 I 0
I 0 I 2 0 0 0 0
the language processing system. Since the task chosen in the experiment was off-line in nature these findings do not necessarily force a differential deficit view. In combination, however, with recent on-line results (Friederici, 1983, 1985, Swinney et al., 1986), this conclusion seems more than viable. The findings for the Wernicke’s aphasics indicate that these patients follow a very general strategy for sentence interpretation, which may even be based on cognitive principles. Wernicke’s aphasics show a clear tendency to assign the first noun in a sentence as the agent, independent of the actual word order and the syntactic complexity. These patients do not seem to base their interpretation on cues given by the morphological passive markers, but rather they rely on strategies which may be provided by the central cognitive system. Broca’s aphasics, by contrast, show equal performance for all passive constructions independent of word order and syntactic complexity. Their comprehension performance for passive sentences was remarkably good, suggesting that these patients follow an interpretation principle which requires the recognition of particular closed class elements in the sentence
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surface form. The only structural configuration that remains constant in all six types of passive sentences is the presence of the passive morphology: the auxiliary, the past participle, and the “by-phrase” in which the noun is marked for agenthood by a preposition. Even though it is obvious that agrammatic aphasics are not able to fully use the structural information given by the passive morphology for unambiguous assignment-their performance is not perfect-these patients seem to use a comprehension strategy which considers these elements to mark structure. The presented findings are in variance with the proposal put forward by Caplan (1983) that performance of agrammatic aphasics (English speaking) could be explained by the possible use of conflicting principles, each relying on different cues for interpretation-such as animacy, word order, and local structural cues. When two principles are in conflict, unambigous assignment of thematic roles is not possible. This approach predicts that in the case of reversible passive sentences, where two principles (word order and local structural cues) are in conflict, patients should perform at random-a pattern of performance which was reported for a case of an English-speaking agrammatic patient by Caplan and Futter (1986). The notion of conflicting information has also been used by Grodzinsky (1984) although at a different level of description. He characterizes agrammatism within a particular linguistic theory (Chomsky, 1981), which defines different levels of representation. At one level (s-structure representation) all members of major categories are lexically specified, whereas the restthat is, the closed class items with the exception of some prepositions (which satisfy a particular structural condition )-are specified only by features. What is specified at this level with respect to an English passive sentence are the major category items as well as the preposition by which marks agenthood. It is to this level of representation that agrammatic patients have access. Although Grodzinsky (1984) calls for consistency within the level of description for accounts of aphasic deficits, he leaves the level of linguistic description when he claims that Broca’s aphasics should perform at random with passive sentences in English due to two qualitatively different types of conflicting information: at the level of linguistic representation the patient is able to recognize the by as the sign of agenthood; within the domain of strategic operations, however, a default principle requires that the noun in subject position should be assigned as the agent. Grodzinsky cites the results obtained by Caplan and Futter (1986) as supporting his view. Unfortunately, however, this study does not provide the critical test Grodzinsky would need to show that the default principle operates in the absence of a passive by-phrase. His view would predict agentless passives to be interpreted 100%incorrectly by agrammatics.
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The nonrandom performance for the Dutch-speaking agrammatic Broca’s aphasics observed in the present study, however, can only be explained within either of these approaches if certain interpretation principles are language-specific. Given that Dutch has less strict word order constraints than English, possible conflicts between knowledge about local structural markers such as the passive morphology and some global word order strategy (e.g., agent-first) are less likely to occur in Dutch than in English. One explanation for the findings in both languages could be formulated as follows: agrammatic aphasics are able to recognize those structural elements which play the role of a thematic role assigner such as agent, theme, goal, and others (Rizzi, 1985). However, since access to the structural information of closed class elements is not complete, the language system is not able to construct an adequate structural sentence representation. The incomplete linguistic representation is forwarded to the general cognitive system where interpretation strategies, which are based upon general world knowledge, compensate for missing structural information. Agrammatics’ off-line comprehension performance presented here seems to reflect a specific deficit of the underlying structural processes rather than the application of compensatory strategies. The underlying deficit of agrammatic Broca’s aphasics can be located in the structural domain: the deficit, however, is less general than previously assumed. Agrammatic Broca’s aphasics are able to recognize those closed class elements which assign thematic roles. They are, however, unable to access all features of the structural information given by these elements. Results from this study-in combination with findings from some recent on-line studies (Friederici, 1983: Swinney et al., 1984)-provide evidence for the view that the underlying deficits of Broca’s and Wemicke’s aphasia are of a different type. Pursuing the distinction between underlying language processes and interpretation strategies in a model of language comprehension, the similarities in Broca’s and Wemicke’s aphasics’ comprehension in some off-line tasks are not attributed to a unitary deficit but rather to the use of a number of cognitively based strategies which may sometimes lead to the identical interpretations of given sentences. At present, the deficit underlying the performance of Wemicke’s aphasics remains unspecified. The conclusion that can be drawn from the available on-line and off-line data suggests that Wernicke patients have retained the ability to automatically process elements of either grammatical class in the initial processing phase. Their comprehension difficulties arise at a level where integration of semantic and syntactic information takes place. Interpretation seems to be guided by some general strategies which are part of the cognitive system and which, in the absence of semantic or pragmatic cues, use global structural information about the sequential arrangement of words to assign thematic roles.
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Broca’s aphasics’ processing may be specified as being due to limitations in accessing the full structural information of closed class elements. They are left with the ability to recognize these items’ forms, their lexicalsemantic specifications, their thematic role assigning function, without being able to exploit all aspects of the information given by these items. The observed structural deficit, however, is more restricted than previous views assumed. Future research is clearly necessary to specify these restrictions and their constraints for models of normal language use. REFERENCES Bemdt, R. S., & Caramazza, A. 1980. A redefinition of the syndrome of Broca’s aphasia: Implications for a neuropsychological model of language. Applied Psycholinguistics, 1, 225-278.
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Heeschen, C. 1985. Agrammatism and paragrammatism: A fictitious opposition. In M.-L. Kean (Ed.), Agrammatism. New York: Academic Press.
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Marslen-Wilson, W. D., & Welch, A. 1978. Processing interactions and lexical access during word recognition in continuous speech. Cognitive Psychology, 10, 29-63. Meyer, D. M., Schvaneveldt, R. W. & Ruddy, M. G. 1971. Loci of contextual effects on word recognition. In P. A. M. Rabbitt & S. Dornic (Eds.), Attenfion undperformance (Vol. 5). New York: Academic press. Milberg, W., & Blumstein, S. E. 1981. Lexical decision and aphasia: Evidence for semantic processing. Brain and Lnnguage, 14, 371-385. Parisi, D., & Pizzamiglio, L. 1970. Syntactic comprehension in aphasia. Cortex, 6, 204215. Rizzi, L. 1985. Two notes on the linguistic interpretation of Broca’s aphasia. In M.-L. Kean (Ed.) Agrammarism. New York: Academic Press. Schwartz, M. F., Saffran, E. M., & Marin, 0. S. M. 1980. The word order problem in agrammatism. 1. Comprehension. Brain and Language. 10, 249-262. Shewan, C. M., & Canter, G. J. 1971. Effects on vocabulary, syntax and sentence length on auditory comprehension in aphasic patients. Correx, 7, 209-226. Shiffrin, R. M., & Schneider, W. 1977. Controlled and automatic human information processing II. Perceptual learning, automatic attending and a general theory. Psychological Review,
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