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Biomedical subjects

G Hickok

Publications and source records attributed to G Hickok.

At least 19 recordsLinked to original sources
PubMed2001

Role of anterior temporal cortex in auditory sentence comprehension: an fMRI study.

Recent neuropsychological and functional imaging evidence has suggested a role for anterior temporal cortex in sentence-level comprehension. We explored this hypothesis using event-related fMRI. Subjects were scanned while they listened to either a sequence of environmental sounds describing an event or a corresponding sentence matched as closely as possible in meaning. Both types of stimuli required subjects to integrate auditory information over time to derive a similar meaning, but differ in the processing mechanisms leading to the integration of that information, with speech input requiring syntactic mechanisms and environmental sounds utilizing non-linguistic mechanisms. Consistent with recent claims, sentences produced greater activation than environmental sounds in anterior superior temporal lobe bilaterally. A similar speech > sound activation pattern was noted also in posterior superior temporal regions in the left. Envirornmental sounds produced greater activation than sentences in right inferior frontal gyrus. The results provide support for the view that anterior temporal cortex plays an important role in sentence-level comprehension.

Adult↗
PubMed2001

Functional anatomy of speech perception and speech production: psycholinguistic implications.

This paper presents evidence for a new model of the functional anatomy of speech/language (Hickok & Poeppel, 2000) which has, at its core, three central claims: (1) Neural systems supporting the perception of sublexical aspects of speech are essentially bilaterally organized in posterior superior temporal lobe regions; (2) neural systems supporting the production of phonemic aspects of speech comprise a network of predominately left hemisphere systems which includes not only frontal regions, but also superior temporal lobe regions; and (3) the neural systems supporting speech perception and production partially overlap in left superior temporal lobe. This model, which postulates nonidentical but partially overlapping systems involved in the perception and production of speech, explains why psycho- and neurolinguistic evidence is mixed regarding the question of whether input and output phonological systems involve a common network or distinct networks.

Brain↗
PubMed2000

A functional magnetic resonance imaging study of the role of left posterior superior temporal gyrus in speech production: implications for the explanation of conduction aphasia.

Conduction aphasia, characterized by good auditory comprehension and fluent but disordered speech production, is classically viewed as a disconnection syndrome. We review recent evidence which suggests that at least one form of conduction aphasia results from damage to cortical fields in the left posterior superior temporal gyrus which participate not only in speech perception, but also in phonemic aspects of speech production. As a test of this hypothesis, we carried out a 4T functional magnetic resonance imaging study in which subjects named visually presented objects sub-vocally. Group-based analyses showed that a majority of participants showed activation in two regions on the dorsal portion of the left posterior superior temporal gyrus.

Adult↗
PubMed2000

Towards a functional neuroanatomy of speech perception.

The functional neuroanatomy of speech perception has been difficult to characterize. Part of the difficulty, we suggest, stems from the fact that the neural systems supporting 'speech perception' vary as a function of the task. Specifically, the set of cognitive and neural systems involved in performing traditional laboratory speech perception tasks, such as syllable discrimination or identification, only partially overlap those involved in speech perception as it occurs during natural language comprehension. In this review, we argue that cortical fields in the posterior-superior temporal lobe, bilaterally, constitute the primary substrate for constructing sound-based representations of speech, and that these sound-based representations interface with different supramodal systems in a task-dependent manner. Tasks that require access to the mental lexicon (i.e. accessing meaning-based representations) rely on auditory-to-meaning interface systems in the cortex in the vicinity of the left temporal-parietal-occipital junction. Tasks that require explicit access to speech segments rely on auditory-motor interface systems in the left frontal and parietal lobes. This auditory-motor interface system also appears to be recruited in phonological working memory.

Journal Article↗
PubMed1999

Discourse deficits following right hemisphere damage in deaf signers.

Previous findings have demonstrated that hemispheric organization in deaf users of American Sign Language (ASL) parallels that of the hearing population, with the left hemisphere showing dominance for grammatical linguistic functions and the right hemisphere showing specialization for non-linguistic spatial functions. The present study addresses two further questions: first, do extra-grammatical discourse functions in deaf signers show the same right-hemisphere dominance observed for discourse functions in hearing subjects; and second, do discourse functions in ASL that employ spatial relations depend upon more general intact spatial cognitive abilities? We report findings from two right-hemisphere damaged deaf signers, both of whom show disruption of discourse functions in absence of any disruption of grammatical functions. The exact nature of the disruption differs for the two subjects, however. Subject AR shows difficulty in maintaining topical coherence, while SJ shows difficulty in employing spatial discourse devices. Further, the two subjects are equally impaired on non-linguistic spatial tasks, indicating that spared spatial discourse functions can occur even when more general spatial cognition is disrupted. We conclude that, as in the hearing population, discourse functions involve the right hemisphere; that distinct discourse functions can be dissociated from one another in ASL; and that brain organization for linguistic spatial devices is driven by its functional role in language processing, rather than by its surface, spatial characteristics.

Aged↗
PubMed1998

Auditory evoked M100 reflects onset acoustics of speech sounds.

Magnetoencephalography (MEG) was used to investigate the response to speech sounds that differ in onset dynamics, parameterized as words that have initial stop consonants (e.g., /b/, /t/) or do not (e.g., /m/, /f/). Latency and amplitude of the M100 auditory evoked neuromagnetic field, recorded over right and left auditory cortices, varied as a function of onset: stops had shorter latencies and higher amplitudes than no-stops in both hemispheres, consistent with the hypothesis that M100 is a sensitive indicator of spectral properties of acoustic stimuli. Further, activation patterns in response to stops/no-stops differed in the two hemispheres, possibly reflecting differential perceptual processing for the acoustic-phonetic cues at the onset of spoken words.

Adult↗
PubMed1998

Hemispheric organization of local- and global-level visuospatial processes in deaf signers and its relation to sign language aphasia.

Previous work has shown that deficits in the production and perception of signed language are linked to left hemisphere damage but not right hemisphere damage in deaf lifelong signers, whereas severe deficits in nonlinguistic visuospatial abilities are more frequent following right hemisphere damage than left hemisphere damage in this population. In the present study we investigated the extent to which sign language deficits in deaf individuals can be dissociated from more subtle visuospatial deficits commonly associated with left hemisphere damage in the hearing/speaking population. A group of left- or right-lesioned deaf signers were asked to reproduce (1) two line drawings (a house and an elephant) and (2) four hierarchical figures. Drawings were scored separately for the presence of local vs global features. Consistent with data from hearing patients, left hemisphere-damaged deaf subjects were significantly better at reproducing global-level features, whereas right hemisphere-damaged deaf subjects were significantly better at reproducing local-level features. This effect held for both types of stimuli. Local-level performance in the LHD group did not correlate with performance on sign language tasks, suggesting that language deficits in LHD deaf signers are in fact linguistic specific.

Aged↗
PubMed1998

Mental rotation within linguistic and non-linguistic domains in users of American sign language.

American sign language (ASL) uses space itself to encode spatial information. Spatial scenes are most often described from the perspective of the person signing (the 'narrator'), such that the viewer must perform what amounts to a 180 degrees mental rotation to correctly comprehend the description. But scenes can also be described, non-canonically, from the viewer's perspective, in which case no rotation is required. Is mental rotation during sign language processing difficult for ASL signers? Are there differences between linguistic and non-linguistic mental rotation? Experiment 1 required subjects to decide whether a signed description matched a room presented on videotape. Deaf ASL signers were more accurate when viewing scenes described from the narrator's perspective (even though rotation is required) than from the viewer's perspective (no rotation required). In Experiment 2, deaf signers and hearing non-signers viewed videotapes of objects appearing briefly and sequentially on a board marked with an entrance. This board either matched an identical board in front of the subject or was rotated 180 degrees. Subjects were asked to place objects on their board in the orientation and location shown on the video, making the appropriate rotation when required. All subjects were significantly less accurate when rotation was required, but ASL signers performed significantly better than hearing non-signers under rotation. ASL signers were also more accurate in remembering object orientation. Signers then viewed a video in which the same scenes were signed from the two perspectives (i.e. rotation required or no rotation required). In contrast to their performance with real objects, signers did not show the typical mental rotation effect. Males outperformed females on the rotation task with objects, but the superiority disappeared in the linguistic condition. We discuss the nature of the ASL mental rotation transformation, and we conclude that habitual use of ASL can enhance non-linguistic cognitive processes thus providing evidence for (a form of) the linguistic relativity hypothesis.

Adult↗
PubMed1996

The neurobiology of sign language and its implications for the neural basis of language.

The left cerebral hemisphere is dominant for language, and many aspects of language use are more impaired by damage to the left than the right hemisphere. The basis for this asymmetry, however, is a matter of debate; the left hemisphere may be specialized for processing linguistic information or for some more general function on which language depends, such as the processing of rapidly changing temporal information or execution of complex motor patterns. To investigate these possibilities, we examined the linguistic abilities of 23 sign-language users with unilateral brain lesions. Despite the fact that sign language relies on visuospatial rather than rapid temporal information, the same left-hemispheric dominance emerged. Correlation analyses of the production of sign language versus non-linguistic hand gestures suggest that these processes are largely independent. Our findings support the view that the left-hemisphere dominance for language is not reducible solely to more general sensory or motor processes.

Adult↗
PubMed1996

Comprehension of wh-questions in two Broca's aphasics.

This study investigated comprehension of wh-questions in two Broca's aphasics. Patients were presented for comprehension with two types of wh-questions: questions headed by which and questions headed by who. These two types were chosen because according to recent syntactic analyses they give rise to different types of syntactic "chains." These questions were presented in both subject gap versions (e.g., which cat chased the dog?) and object gap versions (e.g., which cat did the dog chase?). Comprehension of which questions was asymmetric, with subject gap versions comprehended significantly better than object gap versions, the latter yielding chance-level performance. This finding is consistent with previous reports of subject-object asymmetries in comprehension of relative clauses and clefts, as well as active-passive comprehension asymmetries. In contrast, comprehension of who questions was symmetrical over subject gap and object gap versions: Both patients performed equally well (significantly better than chance) on subject gap and object gap who questions. These findings are inconsistent with current formulations of "chain" or "trace"-based theories of agrammatic comprehension which assume a deficit that affects both types of syntactic chains. We suggest that linguistic descriptions of agrammatic comprehension should be limited to deficits involving only one type of chain. We also suggest that there are processing differences underlying the syntactic distinctions between which-type and who-type questions and that this may account for different patterns of comprehension on these and other constructions.

Aged↗
PubMed1996

Recency preference in the human sentence processing mechanism.

Cuetos and Mitchell (1988) observed that in constructions in which a relative clause can attach to one of two possible sites, English speakers prefer the more recent attachment site, but Spanish speakers prefer the least recent attachment site, in violation of the proposed universal principle Late Closure (Recency Preference), which favors attachments to the most recent sites. Based on this evidence, Cuetos and Mitchell concluded that Late Closure is not a universal principle of the human sentence processing mechanism. In this paper, we provide new evidence from Spanish and English self-paced reading experiments on relative clause attachment ambiguities that involve three possible attachment sites. The results of our experiments suggest that a principle like Late Closure is in fact universally operative in the human parser, but that it is modulated by at least one other factor in the processing of relative clause attachment ambiguities. We propose that the second factor involved in the processing of these and related constructions is the principle of Predicate Proximity, according to which attachments are preferred to be as structurally close to the head of a predicate phrase as possible, and we further consider the origins and predictions of the theory combining these two factors.

Cognition↗
PubMed1995

Representation, referentiality, and processing in agrammatic comprehension: two case studies.

A number of investigators have argued that agrammatic comprehension, the pattern of sentence comprehension often associated with Broca's aphasia, can be characterized in terms of a representational disruption in one or another module of the normal grammar. In this study, these proposals are reviewed and their adequacy is examined in light of two case studies of agrammatic comprehension. In particular, we present data from sentences that have composed the core of the agrammatic comprehension pattern, as well as data from three different classes of sentences including comprehension of the matrix clause of center-embedded relative constructions, pronoun and anaphor dependencies, and Wh-questions. Our conclusion is that none of the existing representational models provides a fully adequate account of the data, and we propose some alternative approaches that distinguish between referential and nonreferential elements and potential processing differences between the two.

Aged↗
PubMed1995

A case of 'sign blindness' following left occipital damage in a deaf signer.

We report on a right-handed, deaf, life long signer who suffered a left posterior cerebral artery (PCA) stroke. The patient presented with right homonymous hemianopia, alexia and a severe sign comprehension deficit. Her production of sign language was, however, virtually normal. We suggest that her syndrome can be characterized as a case of 'sign blindness', a disconnection of the intact right hemisphere visual areas from intact left hemisphere language areas. This case provides strong evidence that the neural systems supporting sign language processing are predominantly in the left hemisphere, but also suggests that there are some differences in the neural organization of signed vs spoken language within the left hemisphere.

Female↗
PubMed1993

Structural description of agrammatic comprehension.

The trace-deletion hypothesis (Grodzinsky, 1990) holds that the comprehension deficit apparent in most agrammatic aphasics results from the absence of traces at the level of S-structure. This paper reports a test of this hypothesis in a case study of an agrammatic aphasic. Two experiments--one using a sentence-picture matching task, one using the truth-value judgment task-examined the comprehension of the matrix clause in center-embedded relatives such as, The tiger that chased the lion is big. These structures provide a crucial test of the trace-deletion hypothesis because comprehension of the matrix clause (i.e., knowing that the tiger is big and not the lion) is predicted to be unimpaired. Contrary to this prediction, however, the results of the present work show that comprehension of the matrix clause in such sentences is significantly impaired. We argue that a revised version of the trace-deletion hypothesis proposed by Hickok (1992a,b) can explain the present data and other previously unaccountable findings.

Aged↗