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Biomedical subjects

J Sergent

Publications and source records attributed to J Sergent.

At least 55 records · Page 3Linked to original sources
PubMed1984

An investigation into component and configural processes underlying face perception.

The nature of the processes underlying face perception was examined in two different paradigms using the same set of stimuli varying on three dimensions of two values each. In a simultaneous matching task, both latencies and errors were found to decrease as the number of differences between stimuli increased. Regression analyses showed that the manipulated features interactively contributed to these variations when the faces were presented in their normal upright orientation, whereas no evidence of an interactive processing was found when the faces were inverted. A multidimensional scaling analysis of dissimilarity judgements between pairs of different upright faces revealed that the overall impression of a face was not simply the sum of subimpressions, and that a configuration typical of each face emerged from the relationship among their particular features, giving each face its individuality. The results suggest that faces have both component and configural properties and lend themselves to different processing strategies that are not mutually exclusive and can unfold simultaneously. Some implications of these results for current research on face perception and recognition are outlined.

Adult↗
PubMed1984

[2-dimensional echography in the preoperative evaluation of mitral stenosis].

2D echocardiography has become one of the most important investigations in the preoperative assessment of mitral stenosis. This study was undertaken to determine the reliability of the information so obtained, by comparison with the surgical appearances. The study population consisted of 104 patients (average age 45 years, 76% women) undergoing open heart surgery for pure mitral stenosis (72%) or mixed mitral valve disease (28%) between 1980 and 1981. All underwent 2D echo using a phased array Aloka SSD 800 80 degrees sector scanner. Cardiac catheterisation was performed in 102 cases and left ventricular angiography in 89 cases. The echocardiogramme was interpreted by an observer who had no knowledge of the surgical results. The mitral surface area, the condition of the valves and subvalvular apparatus and the predictive value of the possible surgical technique were analysed. The 2D echo mitral surface area was estimated by planimetry and quantitatively by using the Gorlin formula during catheterisation and by the surgical description preoperatively. 2D echo was more sensitive than M mode in the detection of severe mitral stenosis (90% vs 73%, p less than 0,01). The 2D echo-Gorlin correlation was quite good (R = 0,70, p less than 0,01) but was worse when the valves were very thickened. When compared with the surgical observations, 87% of the 2D echo data was correct. The thickness of the valves, their amplitude, the diastolic bowing of the anterior leaflet and the presence of calcification were assessed by 2D echo. The echo-surgical results matched perfectly in 76% of cases. The usual cause of error was underestimation of the degree of valvular damage. The valvular bowing and thickness were the most useful signs. Dense, brilliant echos of valvular calcification were found in only 58% of surgically proven cases of valvular calcification, but the error was often related to fine calcification, not visible on fluoroscopy, or to its localisation on the posterior leaflet. The subvalvular apparatus was evaluated in over 93% of patients, a complete study being possible in 73% of them. The 2D echo-surgical correlations were excellent in 90% of the cases in which it had been completely visualised. The chordal thickening was correctly predicted in 79% of cases. The surgical assessment was more pessimistic in 1/3 of cases in which the chordae appeared to be of normal thickness. The length of the chordae was correctly predicted in 68% of cases. The surgical assessment was more pessimistic in 1/2 of cases in which the chordae appeared to be of normal length.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1983

Perceptual categorization in the cerebral hemispheres.

The suggestion of a functional hemispheric dissociation in performing perceptual categorization was examined in two tachistoscopic experiments with normal adults. Subjects were required to match physically identical or similar, but nonidentical, pictures of animals. The first experiment showed no hemispheric difference and indicated that both hemispheres could resort to two different types of categorization process as a function of the simultaneous or delayed mode of presentation of the stimuli. In the second experiment, the viewing conditions were manipulated so as to afford a reduced amount of stimulus energy, and a significant left-visual-field advantage was then obtained. The results are discussed with respect to models of information processing in the cerebral hemispheres, and in relation to impairments in object recognition following brain damage.

Adolescent↗
PubMed1982

About face: left-hemisphere involvement in processing physiognomies.

Three experiments were concluded to investigate the involvement of the two cerebral hemispheres in processing faces. Perceptual discrimination of pairs of faces was equally speedy overall when the stimuli were presented in the right visual field (RVF) or left visual field (LVF). For faces differing in one or two features, however, a qualitatively different pattern of results was obtained for the two visual fields, and an RVF advantage emerged when the difference lay in the upper part of the faces (Experiment 1). An examination of the discriminability of the facial features from which the faces were constructed (Experiment 2) showed that the processes involved in RVF comparisons of faces were not dependent on the saliency of the features but, rather, followed a top-to-bottom serial analysis of the stimuli; the speed of the processing involved in LVF presentations was a function of the degree of similarity of the different comparison faces. Evidence for a serial type of comparison faces were used (Experiment 3). It was concluded that even though comparisons were equally speedy overall in LVF and RVF presentations, qualitatively different processes take place in the two hemispheres, which prove competent at processing faces, each in its own way. Some methodological problems inherent in tachistoscopic studies are discussed, and it is proposed that the quality of the stimulus representation achieved or required for cognitive processing may be determinant in the emergence of functional hemispheric asymmetries.

Adult↗
PubMed1982

The cerebral balance of power: confrontation or cooperation?

Two visual search experiments were carried out using as stimuli large letters made of small identical letters presented in right, or left, or central visual fields. Considering the spatial frequency contents of the stimuli as the critical variable, Experiment 1 showed that a left-field superiority could be obtained whenever a decision had to be made on a large (low frequency) letter alone, and a right-field advantage emerged when a small (high frequency) letter had to be processed. Experiment 2 showed that the two levels of structure of the stimulus were not encoded at the same rate and that at very brief exposure, only the large letter could be accurately identified. This was accompanied by a left-field superiority, whether or not the stimulus contained the target. These results are interpreted as revealing a differential sensitivity of the hemispheres to the spatial frequency contents of a visual image, the right hemisphere being more adept at processing early-available low frequencies and the left hemisphere operating more efficiently on later-available low frequencies. From these and other experiments reviewed, it is suggested that (a) cerebral lateralization of cognitive functions results from differences in sensorimotor resolution capacities of the hemispheres; (b) both hemispheres can process verbal and visuospatial information, analytically and holistically; (c) respective hemispheric competence is a function of the level of sensorimotor resolution required for processing the information available.

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

Unified response to bilateral hemispheric stimulation by a split-brain patient.

Surgical sectioning of the corpus callosum in epileptic patients has provided a unique opportunity to study separately the competence and processing capacities of the two cerebral hemispheres, each of which is able to perceive, think, memorize and learn independently and essentially outside the realm of awareness of the other. While research has focused on this 'disconnection syndrome', split-brain patients nonetheless behave as unified individuals in their normal environment, and the present study investigated this aspect of their behaviour in an experimental setting. The two hemispheres of a callosotomized patient were simultaneously presented with information associated with conflicting responses, and the subject was requested to produce a single response. In all combinations of hemisphere stimulation and hand responding, the subject was capable of perfect accuracy, suggesting that he could integrate and resolve the conflicting information before the production of his response, and that his two disconnected hemispheres were simultaneously aiming at the same goal.

Adult↗
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↗