Predicate-argument structure as a link between linguistic and nonlinguistic representations

We present a study wherein a severe Broca's aphasic patient was trained to learn symbols representing both pure transitive and dative predicates--predicates differing in argument structure--in a visually based artificial language (c-ViC). We found a decrease in performance when two symbols, rather than one, were used to depict these "verbs." However, this decrease in performance was more pronounced for symbols representing pure transitive verbs--those that allow only one argument structure--than for symbols representing dative verbs--those that allow two different argument structures. Also, dative "verbs" yielded better performance when they were inserted in more complex, three-argument "sentences" than when they were inserted in two-argument "sentences." The opposite pattern was found for pure transitives. These results are discussed in terms of our claim that argument structure serves as a point of connection between linguistic information and non-linguistic visual information and in terms of the possibility that argument structure entries are shaped by the form in which visual information is parsed.     

Effects of sentential stress and word class upon comprehension in Broca's aphasics

The roles which word class (open/closed) and sentential stress play in the sentence comprehension processes of both agrammatic (Broca's) aphasics and normal listeners were examined with a word monitoring task. Overall, normal listeners responded more quickly to stressed than to unstressed items, but showed no effect of word class. Aphasics also responded more quickly to stressed than to unstressed materials, but, unlike the normals, responded faster to open than to closed class words regardless of their stress. The results are interpreted as support for the theory that Broca's aphasics lack the functional underlying open/closed class word distinction used in word recognition by normal listeners.     

The existence of comprehension patterns in Broca's aphasia.

Berndt and Caramazza (1999) claim that Grodzinsky, Pi?ango, Zurif, and Drai (1999) were able to show a canonical-noncanonical difference (e.g., actives vs. passives) in the comprehension of Broca's aphasic patients only because of a patient selection bias. We show that the canonical-noncanonical comprehension pattern exists apart from any such bias, and that this pattern bears importantly on our understanding of the neuroanatomical organization of comprehension capacity at the sentence level.     

The critical role of group studies in neuropsychology: comprehension regularities in Broca's aphasia

We reexamine the empirical record of the comprehension abilities of Broca's aphasic patients. We establish clear, commonly accepted, selection criteria and obtain a pool of results. We then subject these results to a detailed statistical analysis and show that these patients comprehend certain canonical sentences (actives, subject relatives, and clefts with agentive predicates) at above-chance levels, whereas comprehension of sentences that contain deviations from canonicity (passives, object-gap relatives, and clefts) is distinct and is at chance. That the latter is the case, and patients indeed guess at such structures, we show by comparing the distribution of individual results in passive comprehension to that of a model for such guessing-an analogous series of tosses of an unbiased coin. The two distributions are virtually identical. We conclude that the group's performance is stable, and well-delineated, despite intersubject variation whose source is now identified. This means that certain comprehension tests may not always be used for the diagnosis of individual patients, but they do characterize the group. It also means that group studies are not just a valid option in neuropsychology; they are a must, since demonstrations like ours indiciate very clearly that single-case studies may be misleading. As we show, the findings from any one patient, without the context of a group, may give a distorted picture of the pathological reality. Our conclusions thus promote studies of groups of brain-damaged patients as a central tool for the investigation of brain/behavior relations.     

Slowed lexical access in nonfluent aphasia: a case study.

A list priming paradigm (LPP) was used to examine the hypothesis that nonfluent aphasics are literally slowed down in automatic access to lexical information. In this paradigm, words are presented visually, and the subject's task is to make a lexical decision on each word as quickly as possible after its presentation. As soon as a lexical decision is made on one word, that word is removed and, after a predetermined interword interval, the next word is presented. In this way, a continuous "list" effect is obtained. Prior studies with both college-age and elderly subjects using the LPP have shown that, independently of age, on the LPP, priming obtains at interword delays of 500 to 800 msec, but not at either shorter or longer interword delays. In the study reported here, the LPP was used to examine delays at which priming obtained for LD, a nonfluent aphasic with a lesion primarily in the left frontal region. Examining interword delays ranging from 500 to 1800 msec, the subject showed priming only at a delay of 1500 msec, a considerably longer delay than that at which neurologically intact subjects have shown priming. Based on these results, it is argued that while automatic access is retained, that access is much slower in a nonfluent aphasic than in neurologically intact elderly subjects. These results are discussed in terms of how slowed lexical access might impact on discourse comprehension.     

Speed of Lexical Activation in Nonfluent Broca''s Aphasia and Fluent Wernicke''s Aphasia

Rapid, automatic access to lexical/semantic knowledge is critical in supporting the tight temporal constraints of on-line sentence comprehension. Based on findings of “abnormal” lexical priming in nonfluent aphasics, the question of disrupted automatic lexical activation has been the focus of many recent efforts to understand their impaired sentence comprehension capabilities. The picture that emerges from this literature is, however, unclear. Nonfluent Broca's aphasic patients showinconsistent,notabsent,lexical priming, and there is little consensus about the conditions under which they do and do not prime. The most parsimonious explanation for the variable findings from priming studies to date is that the primary disturbance in Broca's lexical activation has something to do withspeedof activation. Broca's aphasic patients prime when sufficient time is allowed for activation to spread among associates. To examine this “slowed activation” hypothesis, the time course of lexical activation was examined using a list priming paradigm. Temporal delays between successive words ranged from 300 to 2100 msec. One nonfluent Broca's aphasic patient and one fluent Wernicke's patient were tested. Both patients displayed abnormal priming patterns, though of different sorts. In contrast to elderly subjects, who prime at relatively short interstimulus intervals (ISIs) beginning at 500 msec, the Broca's aphasic subject showed reliable automatic priming but only at a long ISI of 1500 msec. That is, this subject retained the ability to access lexical information automatically if allowed sufficient time to do so, a finding that may help explain disrupted comprehension of normally rapid conversational speech. The Wernicke's aphasic subject, in contrast, showed normally rapid initial activation but continued to show priming over an abnormally long range of delays, from 300 msec through 1100 msec. This protracted priming suggests failure to dampen activation and might explain the semantic confusion exhibited by fluent Wernicke's patients.     

Hemispheric specialization for the perception of speech sounds: The influence of intonation and structure

The present report investigates the effect of various cues to phrase structure upon the hemispherically lateralized processing of phonetic structure. Meaningless sequences were paired for dichotic presentation and were delivered under two different conditions termed structured and semistructured. The dichotic sequences in the two conditions contained the same nonsense syllable stems, English bound morphemes, and English function words. Also each of the sequences in both conditions were grammatically ordered in the sense that if the nonsense stems were replaced by English stems, a grammatical sentence would result. The conditions differed with respect to prosody, however: the structured sequences were characterized by the acoustic correlates of constituent structure; the semistructured sequences were delivered in a monotone. A significant right-ear superiority was observed in the structured condition, but not in the semistructured condition. These perceptual laterality differences are discussed in relation to cerebral dominance for language and in relation to speech processing generally.