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J Sergent

Publications and source records attributed to J Sergent.

12 recordsLinked to original sources
PubMed1992

Distributed neural network underlying musical sight-reading and keyboard performance.

Music, like other forms of expression, requires specific skills for its production, and the organization and representation of these skills in the human brain are not well understood. With the use of positron emission tomography and magnetic resonance imaging, the functional neuroanatomy of musical sight-reading and keyboard performance was studied in ten professional pianists. Reading musical notations and translating these notations into movement patterns on a keyboard resulted in activation of cortical areas distinct from, but adjacent to, those underlying similar verbal operations. These findings help explain why brain damage in musicians may or may not affect both verbal and musical functions depending on the size and location of the damaged area.

Auditory Perception↗
PubMed1992

Functional and anatomical decomposition of face processing: evidence from prosopagnosia and PET study of normal subjects.

Studies of brain-damaged patients have revealed the existence of a selective impairment of face processing, prosopagnosia, resulting from lesions at different loci in the occipital and temporal lobes. The lesions are often extensive, and it is unclear what functional aspects of face processing are normally served by the damaged areas, and whether they are uniquely devoted to the processing of faces. These issues are further addressed through a combined magnetic resonance imaging (MRI) and positron emission tomography (PET) study of regional cerebral blood flow (rCBF) in normal subjects performing different tasks of face and object processing. The results indicate different patterns of cerebral activation depending on the requirements of the tasks within the processing of faces, as well as a clear dissociation of the neural substrates underlying face and object processing. These results are compared with radiological data from prosopagnosic patients, and are put in relation with the patterns of deficits observed in the patients as a function of the location of their lesions. Together, the findings offer new evidence regarding the functional neuroanatomy of face and object processing.

Agnosia↗
PubMed1992

Judgements about numerosity by a commissurotomized subject.

A commissurotomized subject, L.B., was shown asterisks flashed at random locations, up to four in each field, and attempted either to compare the numbers in the two fields or to report the total number. The main results were: (a) Report was more accurate with unilateral than with bilateral presentation, suggesting that the difficulty integrating across fields was partly attentional; (b) in integrating across fields, attention was focused on one field, with only crude 'one-or-many' information from the other; (c) in cross-field comparisons, the focus was on the LVF, but in reporting the number it was on the RVF when report was oral or right-handed, and on the LVF when report was left-handed; (d) cross-field comparisons were improved when the locations were mirrored across the midline.

Adult↗
PubMed1992

Face recognition.

The study of face-selective neurons in the monkey temporal lobe, and face recognition deficits in humans after brain damage have both become very active fields of investigation. Face-selective neurons appear to be members of ensembles for coding faces rather than individual face detectors or grandmother cells. They reflect the more general role of temporal cortex in pattern recognition. In humans there are a variety of face-processing impairments that result from damage to different areas, and which reflect interference at different levels of processing of the facial image.

Animals↗
PubMed1992

Functional neuroanatomy of face and object processing. A positron emission tomography study.

Studies of brain-damaged patients have revealed the existence of a selective impairment of face processing, prosopagnosia, resulting from lesions at different loci in the occipital and temporal lobes. The results of such studies have led to the identification of several cortical areas underlying the processing of faces, but it remains unclear what functional aspects of face processing are served by these areas and whether they are uniquely devoted to the processing of faces. The present study addresses these questions in a positron emission tomography (PET) study of regional cerebral blood flow in normal adults, using the 15 oxygen water bolus technique. The subjects participated in six tasks (with gratings, faces and objects), and the resulting level of cerebral activation was mapped on images of the subjects' cerebral structures obtained through magnetic resonance and was compared between tasks using the subtraction method. Compared with a fixation condition, regional cerebral blood flow (rCBF) changes were found in the striate and extrastriate cortex when subjects had to decide on the orientation of sine-wave gratings. A face-gender categorization resulted in activation changes in the right extrastriate cortex, and a face-identity condition produced additional activation of the fusiform gyrus and anterior temporal cortex of both hemispheres, and of the right parahippocampal gyrus and adjacent areas. Cerebral activation during an object-recognition task occurred essentially in the left occipito-temporal cortex and did not involve the right hemisphere regions specifically activated during the face-identity task. The results provide the first empirical evidence from normal subjects regarding the crucial role of the ventro-medial region of the right hemisphere in face recognition, and they offer new information about the dissociation between face and object processing.

Adult↗
PubMed1991

Judgments of relative position and distance on representations of spatial relations.

This article examines Kosslyn's (1987) hypothesis of the unequal capacity of cerebral hemispheres to process categorical and coordinate spatial relations. Experiment 1 comprised 4 different tasks and failed to support this hypothesis in normal Ss. With the same stimulus patterns as in Kosslyn's study, the results failed to confirm cerebral asymmetry for representing the 2 types of spatial relations, in normal (Experiment 2) and commissurotomized (Experiment 3) Ss. In Experiment 4, a reduction in stimulus luminance produced a partial confirmation of the hypothesis as the right hemisphere proved more adept than the left hemisphere at operating on coordinate representations, whereas both were equally competent at processing categorical spatial-relation representations. The results suggest that the 2 hemispheres can operate on both types of spatial relations, but their respective efficiency depends on the quality of the representations to be processed.

Adult↗
PubMed1991

Processing of spatial relations within and between the disconnected cerebral hemispheres.

This study examined three issues related to the processing of spatial relations by commissurotomized subjects. One issue was concerned with the respective competence of the disconnected cerebral hemispheres at performing judgements of relative position and distance between 2 objects appearing at varying locations in the visual space. Contrary to recent suggestions, the results showed that the two hemispheres were equally competent at representing categorical and coordinate spatial relations and at operating on these representations. The second issue was concerned with the capacity of the two disconnected hemispheres to operate conjointly. The subjects were simultaneously presented with the same information in the two visual fields and were required to produce a single response based on this information. Compared with unilateral presentations, bilateral presentations resulted in enhanced response accuracy and, depending on the type of decision, in patterns of response latency and accuracy different from the patterns of either unilateral condition. These results suggest that the two disconnected hemispheres can operate simultaneously and are able to join the outcomes of their respective operations before the production of a single response. The third issue was concerned with interhemispheric communication of visuospatial information. Unlike pattern information that is typically confined to the hemisphere that receives it in the commissurotomized brain, visuospatial information could be subjected to interhemispheric comparison as a function of its categorical and metric properties, although the patients had only implicit knowledge of part of the transferred information. Implications of these findings for the contribution of the hemispheres to visuospatial processing and for the understanding of the functioning of the commissurotomized brain are discussed.

Adult↗
PubMed1979

On the use of symmetry in the Rorschach Test.

Rorschach's justifications for the use of symmetry in his inkblots are evaluated in the light of recent empirical research concerning the perception of symmetry. The role of symmetry in response facilitation, in the production of whole and movement responses, in the creation of similar conditions for left- and right-handers, and as a response determinant, is discussed and re-evaluated.

Eye Movements↗
PubMedDate not supplied

Positron emission tomography study of letter and object processing: empirical findings and methodological considerations.

The study of functional-anatomical correlations of higher-order cognitive processing has benefited from recent advances in brain imaging techniques such as positron emission tomography (PET) measurements of regional cerebral blood flow (CBF). Comparisons of CBF changes by paired image subtraction provide the opportunity to isolate cerebral areas participating in the realization of the processes that differentiate two tasks. However, the subtraction method is based on assumptions that are not entirely compatible with cerebral cognitive processing, and the derived pattern of activation specifically associated with the processes that differentiate two tasks is relative to the activation associated with the subtracted task and may therefore vary as a function of the processes actually performed in this subtracted task. To examine the implications of this procedure, a PET study with the 15O water bolus technique was carried out on normal adults. Subjects performed three tasks that made nonoverlapping cognitive processing demands: a semantic categorization of visual objects, a spatial discrimination of visually presented letters, and a phonological decision on visually presented single letters. Each task produced distinct patterns of activation consistent with evidence from neurological patients, specifically in the left occipital cortex in the semantic categorization of objects, in the parietal cortex of both hemispheres in the letter-spatial task, and in the left frontal and superior temporal cortex in the letter-sound task. However, the comparisons between the two letter tasks did not result in the expected CBF changes even though these two tasks make distinct processing requirements and are dissociable by brain injury. In addition, the phonological task resulted in activation of areas of the frontal cortex that earlier PET studies had identified as participating in semantic operations, whereas letters have no semantic property. These results suggest that the interpretation of patterns of activation is confronted with difficulties due to the automatic, and uncontrolled, processing of verbal stimuli that raises the threshold for significant CBF changes between two conditions that use the same stimuli but different task demands.

Adult↗
PubMedDate not supplied

Varieties of functional deficits in prosopagnosia.

Prosopagnosia is a neurologically based deficit characterized by the inability to recognize faces of known individuals in the absence of severe intellectual, perceptual, and memory impairments. The nature of the underlying disturbance was investigated in three patients in an attempt to identify the structural and functional levels at which the processing of faces breaks down, the relation between prosopagnosia and associated deficits, and the specificity of the prosopagnosic disturbance. The breakdown of face processing resulted from unilateral damage in different cerebral structures of the right hemisphere in the three patients, and it involved different functional levels of face processing, but all three patients displayed perceptual impairments of unequal severity. In one patient (R.M.), the deficit encompassed all perceptual operations on faces, including matching identical views of the same faces, but it did not extend to all categories of objects characterized by a close similarity among their instances; the second patient (P.M.) exhibited a less severe perceptual impairment but was unable to derive the configurational properties from a facial representation and to extract its physiognomic invariants; the third patient (P.C.) had not lost the capacity to differentiate faces on the basis of their configurations but could not associate a facial representation with its pertinent memories. Associated deficits were present in each patient but differed depending on the anatomofunctional locus of the breakdown, although all patients were impaired at recognizing noncanonical views of objects that they readily recognized when shown from a conventional viewpoint. However, performance dissociation within patients and double dissociation between patients suggest that these associated deficits are not necessary concomitants of prosopagnosia.

Agnosia↗
PubMedDate not supplied

Implicit access to knowledge derived from unrecognized faces in prosopagnosia.

Prosopagnosia is an acquired neurological impairment characterized by an inability to experience a feeling of familiarity at the view of faces of known individuals and to identify these individuals. The inability of prosopagnosic patients to recognize faces does not entail that perceived faces go unprocessed in their brains, and there are indications that cognitive operations are still performed whereby a perceived face reactivates pertinent memories, but either these operations cannot be completed or their outcome fails to reach consciousness. A series of experiments were conducted on three severe prosopagnosic patients in an attempt to understand better this phenomenon known as covert face recognition, the conditions for its occurrence, and its functional locus. The capacity of the patients implicitly to access pertinent knowledge related to overtly unrecognized faces was inversely related to the severity of their perceptual deficit, suggesting that some preserved ability to extract the physiognomic invariants of a face is a necessary condition for the occurrence of the phenomenon. However, the results indicated that covert recognition does not take place at a perceptual or structural level although it is initiated at such a level, that it may have more than one underlying mechanism, and that it is achieved through the reactivation of specific information related to the individual's identity. Under special conditions that restricted the relevant knowledge that needed to be activated, transient overt recognition of faces was experienced by one of the prosopagnosic patients.

Agnosia↗