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Biomedical subjects

J Sergent

Publications and source records attributed to J Sergent.

At least 19 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↗
PubMed1990

The neuropsychology of visual image generation: data, method, and theory.

This paper presents a review of the empirical evidence bearing on the localization of the image-generation process in cerebral structures and examines several issues related to the study of functional hemispheric asymmetry. In spite of recent claims that the left hemisphere is specialized for the generation of mental visual images, an examination of the relevant data and experimental procedures provides little support for this view and suggests that both hemispheres simultaneously and conjointly contribute to this process. Methodological and theoretical issues related to the localization of functions in the brain, some assumptions guiding laterality research, and computational models of cerebral lateralization are briefly discussed.

Brain↗
PubMed1990

Furtive incursions into bicameral minds. Integrative and coordinating role of subcortical structures.

Section of forebrain commissures results in a pervasive disconnection syndrome characterized by the incapacity of the two cerebral hemispheres to exchange their respective information content. Yet commissurotomized patients are capable of unified behaviour in their daily activities and, in laboratory situations, are able to produce a single response as a function of the information received by both hemispheres. This study further investigated the nature of the information that can be communicated between the disconnected hemispheres in 3 commissurotomized patients. The first part comprised 7 experiments in which the patients were required to compare 2 digits simultaneously, 1 projected to each hemisphere. While the stimulus and experimental conditions were the same across experiments, the information content on which to base the comparison was manipulated. The level of performance varied as a function of the information content, such that the patients were unable to decide whether the 2 digits were the same or different, performed better when required to compare the digits in terms of their odd-even category, and were highly accurate at deciding which digit was the higher. In addition, when instructed to focus on the numerical value of the digits to decide whether the 2 digits were the same or different, they performed significantly above chance. In the second part, they were requested to report verbally information about emotional faces and familiar faces projected to the right hemisphere. While they were unable to access the visual characteristics and the identity of the faces, they could provide various correct items of semantic information about the individuals. Taken together, the results indicate that the disconnection syndrome is limited to specific categories of information and does not extend to all the knowledge that may be derived from a given object. They also suggest that subcortical structures do not serve simply as pathways linking the two hemispheres but play an essential coordinating role in the integration of hemisphere activity.

Brain↗
PubMed1990

From covert to overt recognition of faces in a prosopagnosic patient.

Prosopagnosia is an inability to recognize known persons as a result of a failure to access relevant memories through the inspection of their faces. The nature of this disturbance, and the fate of memories related to faces, were investigated in a long-standing prosopagnosic woman (P.V.). An examination of P.V.'s perceptual capacities indicated no major impairment at matching faces, including different views of the same faces, and multidimensional scaling analysis showed that she could achieve configurational representations of faces as do normal subjects. In spite of her inability to evoke memories of known persons from their faces, P.V. displayed clear evidence that she could use pertinent memories related to these faces in tasks that did not explicitly call for their evocation. This covert recognition of faces was observed in perceptual learning and cued-recognized faces, attempts were made at surmounting the blocked activation of pertinent memories. Some of these attempts were successful in inducing P.V. into experiencing a sense of familiarity with the faces and identifying them, and this was the first occurrence of overt face recognition by P.V. since the onset of her illness. These findings provide clarification of the nature of the prosopagnosic disturbance and new information about the processes by which faces are recognized. They suggest that (1) prosopagnosia may result from a breakdown at different levels of face-recognition processes, (2) prosopagnosia may occur in spite of normal configurational encoding of facial representations, (3) covert recognition of overtly unrecognized faces requires the integrity of perceptual processes, and (4) failure of overt face recognition reflects a disturbance in the normal interactions between pertinent memories and facial representations which thus remain meaningless.

Agnosia↗
PubMed1989

Mental rotation in a commissurotomized subject.

The commissurotomized subject L.B. showed a strong right-hemispheric advantage on a task requiring him to judge rotated letters normal or backward, but a left-hemispheric advantage in a task requiring discrimination of the same letters, implying that the right-hemispheric advantage has to do with mental rotation. However, his right hemisphere proved unable to perform a task requiring mental rotation of a simple unfamiliar pattern to a designated "upright", and was inferior to the left on a task requiring two such patterns, at varying orientations relative to one another, to be judged same or different. We suggest that the deficiency of the right hemisphere on these tasks was unrelated to mental rotation per se, but reflected a failure to comprehend the tasks properly.

Adult↗
PubMed1989

Hemispheric specialization for mental rotation.

A sample of 133 normal subjects, and one commissurotomized subject, were given a "mental-rotation" task, in which they were timed as they decided whether rotated letters, flashed in the left or right visual hemifield, were normal or backward. The normal subjects showed a significant right-hemifield advantage in reaction time, while the commissurotomized subject showed a pronounced left-hemifield advantage in both accuracy and reaction time. We argue that mental-rotation is primarily a right-hemispheric specialization, but that this was offset in the normal subjects by a stronger left-hemispheric specialization for letter identification.

Adolescent↗
PubMed1989

Image generation and processing of generated images in the cerebral hemispheres.

Recent computational models describing the contribution of the cerebral hemispheres to visual imagery have suggested an exclusive capacity of the left hemisphere to generate multipart images. A brief review of relevant findings indicates that the evidence presented in support of this suggestion is not entirely compelling; this prompted a reexamination of this issue in a lateral tachistoscopic study on normal adults. Sixteen subjects participated in two experiments in which they had to decide whether or not a lowercase letter contained a segment extending above or below the main body of the letter. This decision was made directly on lowercase letters in one experiment (perceptual task) and on their generated images in the other experiment (imagery task). The quality of the letters (clear or blurred) and the retinal eccentricity of stimulus presentation (small or large) were orthogonally manipulated. The perceptual task yielded no main effect of visual field but a significant interaction of visual field and letter quality. By contrast, the imagery task resulted in a left visual-field superiority but no interaction involving the visual fields--a departure from predictions based on current models of visual imagery. In addition, the pattern of results in the imagery task corresponded to that obtained with blurred letters in the perceptual task, suggesting limitations in spatial resolution of visual images. Implications of these results for models of cerebral lateralization and visual imagery are discussed.

Adult↗
PubMed1989

Categorization of disoriented faces in the cerebral hemispheres of normal and commissurotomized subjects.

We examined the capacity of the cerebral hemispheres to process faces that deviate from canonical perspective. In Experiment 1, normal Ss performed a gender categorization of faces presented at varying angular orientations in the left visual field (LVF) or right visual field (RVF). Orientation affected processing speed, more so in the RVF than in the LVF. The function relating reaction times to disorientation of the faces was approximately monotonic and reflected the increased difficulty in extracting relevant configurational information as the faces were rotated from canonical perspective. In Experiment 2, 3 commissurotomized Ss performed the same task. They responded above chance in the 2 visual fields, and the pattern of their results was similar to that obtained with the normal Ss, but the effect of disorientation was considerably more pronounced. It is suggested that the right hemisphere contribution becomes more critical the further the visual pattern departs from conventional view. Issues regarding the specification of processes correcting for disorientation and comparison of normal and commissurotomized Ss are discussed.

Adult↗
PubMed1989

Prosopagnosia in a right hemispherectomized patient.

The first reported case of prosopagnosia in a right hemispherectomized woman, B.M., whose intellectual and cognitive functions were otherwise normal or only slightly impaired, is presented. She was totally unable to identify, and to experience a sense of familiarity with, faces of persons she knew, but she could evoke semantic information about them and retrieve their names from visual contextual cues. She was unaware that she was lacking face-recognition skills and that faces alone could be used to access the identity of individuals. The functional nature of her deficit was investigated through sensory, perceptual, memory, and learning tasks to determine the level at which her prosopagnosic disturbance occurred. She was defective at resolving low spatial-frequency information, but this was insufficient to explain the selectivity of her impairment. She was able to carry out cognitive operations specific to faces as long as facial identity did not have to be ascertained, and she performed as well as control subjects at deriving information about the gender, age, and emotion of faces. She was impaired at matching different views of the same faces, and multidimensional scaling analysis of dissimilarity judgements between faces indicated an inability to combine the component features into a configurational facial representation that would uniquely define each face. In contrast to recently reported cases of prosopagnosia, B.M. showed no sign of covert recognition of known faces in a learning task, and there was no indication that she could, even for a few seconds, store a faithful facial representation. The occurrence of prosopagnosia in this hemispherectomized patient confirms that this deficit can emerge without damage to the left hemisphere, and her unawareness of her deficit, which had remained unnoticed for several years, raises the possibility that other hemispherectomized patients may be prosopagnosic. The pattern of cognitive impairments displayed by B.M. indicates a perceptual basis to her disturbance and is discussed in relation to other cases of prosopagnosia.

Adult↗
PubMed1985

Influence of task and input factors on hemispheric involvement in face processing.

Two experiments examined the respective role of the cerebral hemispheres in face perception and the nature of their contribution depending on task demands and on the spatial-frequency composition of the stimuli. Sixteen faces of members of the subjects' department were presented as stimuli, with men and women, and professors and nonprofessors being equally represented. In Experiment 1, high-resolution black-and-white photographs of faces were used in three reaction-time tasks: verbal identification, manual membership categorization, and manual male/female categorization, in a within-subject design. Identification and membership categorization were significantly better performed in right-visual-field presentations, whereas the male/female categorization yielded a nonsignificant left-visual-field superiority. In Experiment 2, two versions of the same faces were used: digitized low-pass (0 to 2 cycles/degree of visual angle) and digitized broad-pass (0 to 32 cycles/degree) faces. Broad-pass faces produced the same laterality pattern as in Experiment 1, while low-pass faces were better processed in left-visual-field presentations for all three tasks. The results suggest that the two hemispheres play a role in face perception, and their contribution may vary as a function of the task demands and of the spatial-frequency components of the incoming information.

Adult↗
PubMed1985

[Positive inotropic agents. Generalities and classification].

The aim of inotropic therapy is to increase the force of myocardial fibre shortening by improving the availability of calcium to the contractile proteins. Digitalis remains the most widely used drug, but its positive inotropic effects are weak and the therapeutic index is low. Dobutamine is the most useful catecholamine because the most cardioselective and it induces the least increase in myocardial oxygen consumption. There are three groups of new inotropic agents: sympathomimetics: pirbuterol and prenalterol are effective in the short term but tolerance is usually observed within a few weeks. Salbutamol and terbutaline have only been assessed in acute studies, phosphodiesterase inhibitors (MDL 17043, MDL 19025) are powerful inotropic agents in the short and medium term. ARL 115 has mainly been studied by parenteral administration, Amrinone has a largely unknown mode of action, but is a very effective positive inotropic drug; its side-effects limit it as age. However, its derivative, milrinone, seems to be more inotropic and less toxic. The new inotropic drugs currently under assessment are active in the short term but their long-term efficacy and side-effects are still little known. The ideal inotropic agent remains to be discovered.

Adrenergic beta-Agonists↗