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PubMedDate not supplied

[Electrophysiologic analysis of interhemispheric differences in mechanisms of visual recognition].

During tachistoscopic lateralized presentation of a series of geometrical figures in different conditions of recognition, early and late EP components were analyzed in the occipital, occipito-temporo-parietal, parietal and frontal cortical areas of the left and right cerebral hemispheres in juveniles and adult subjects. In both age groups, the right side dominance of the early EP component, P50-70, was revealed in the caudal cortical parts that may be connected with the predominant role of this hemisphere in the integral description of images. Asymmerty of the frontal associative zones gets formed at the mature age and consists in prevailing of the late EP components of the left frontal zone in comparison with the right one. The data are considered to reflect age-dependent mechanisms of classification type of recognition in the left hemisphere.

Adolescent↗
PubMed1979

Recognition of changes in the dimensions and categories of visual objects.

The aim of the present work is a comparison between recognition with changes in the dimensions of the objects and recognition with changes in the category of the objects. After preliminary training under tachistoscopic ocnditions, to a control set of different contour drawings are added: (1) the same drawings increased or desreased several times; (2) different new drawings with the same size. The percentage of recognized drawings is determined for such exposure time which is needed for the recognition of 60--80 per cent of the drawings in the control set. Recognition is found to be deteriorated in the case of changes both in the dimensions and in the category of the objects, the deterioration being double for the objects with changed category. This fact serves as a basis for rejecting the hypothesis that considerable changes in the dimensions could create new objects for the visual system. It was also found that recognition of pre-trained drawings is either not influenced or comparatively least influenced by the changes in the dimensions and categories. This result is probably due to the specificity of recognition of long trained objects. The results obtained do not contradict the assumption of the participation of spatial consecutive scanning of the iconic memory in the recognition of the spatial properties of visual objects.

Form Perception↗
PubMed1997

Evidence for rapid face recognition from human scalp and intracranial electrodes.

It is still generally believed that complex visual analysis is not carried out within the first 100 ms. Here we show that intra- and extracranial visual evoked potentials (VEPs) differentiate previously seen faces from novel faces as early as 50 ms after stimulus onset. EEG was recorded from scalp electrodes in 12 male healthy volunteers (group I) and intracranially from implanted depth electrodes in the temporal and frontal cortex of seven epilepsy patients (group II). Both groups were engaged in a face recognition task. All subjects showed significant differential responses which occurred very early (50-90 ms) and later (190-600 ms). In group II, the early responses were recorded more frequently in the right hemisphere, whereas the late differential VEPs were found in both hemispheres. Both types of VEPs were more frequent in the temporal neocortex, underlining its role as a major contributor to these fast recognition processes.

Adult↗
PubMed1993

Recognition potential: sensitivity to visual field stimulated.

The recognition potential (RP) was distinguished from P3 and eye blink responses by its sensitivity to visual area stimulated. Images were flashed in upper and lower hemifields. Current source density profiles were computed, using 16 midline scalp electrodes. For P3 and eye blink profiles, the hemifield stimulated was not a significant factor. For the recognition potential, upper and lower field stimulation produced radically different profiles. An improved recognition potential signal was obtained by a new mathematical procedure. It used the difference in sensitivity to visual area stimulated to reject P3 and eye blink responses.

Adult↗
PubMed1997

Examining the right temporal lobe's role in nonverbal memory.

Tests of facial recognition and spatial learning were administered to presurgical patients with unilateral temporal lobe EEG foci. Right temporal lobe patients obtained lower facial recognition scores than left temporal lobe patients. The groups performed equally on the spatial learning test. A factor analysis revealed two independent factors: a general visuospatial factor and a more specific facial identification factor. The findings provide support for the existence of two dissociable visual processing systems. Memory impairments associated with right temporal lobe dysfunction may be characterized as an impairment in a ventral visual processing system responsible for facial memory and pattern recognition.

Adolescent↗
PubMed1999

Prosopagnosia and structural encoding of faces: evidence from event-related potentials.

Event-related brain potentials (ERPs) were recorded in response to unfamiliar faces and to houses from a severely prosopagnosic patient (PHD) and 24 control subjects. For all control subjects, faces elicited an enhanced negativity at lateral temporal electrodes (N170). This component was absent for PHD. Comparable results were obtained in response to inverted faces and houses. A selective deficit in face recognition is therefore reflected by abnormalities in ERP components specific to faces. As PHD was shown to have substantial deficits on tasks requiring the structural analysis of faces, these findings are consistent with the view that the N170 reflects processes involved in the structural encoding of faces, and may be a measure of selective impairments in the analysis of face components.

Adult↗
PubMed1999

Effects of target area and letter complexity on event-related potentials and reaction time.

The idea that an area of the visual field stimulated by a recognizable image activates a corresponding area of neural tissue that generates the recognition potential (RP) was examined. Sixteen subjects detected targets in a stream of non letter character arrays. The targets were one or five rows of a repeated letter (O or G). RT was less for the larger targets and less for O than for G. RP latency differences agreed with the RT differences. RP amplitude was substantially greater for large than for small targets and moderately larger for G than for O. P3 amplitude showed a different relationship. The observed amplitude-latency relationships indicated that differences in stimulus strength were not responsible for the greater RP evoked by the larger targets. The results strengthened the neural area explanation for RP amplitude modulation by the area of the visual fields impinged on by recognizable images.

Adult↗
PubMed1985

Contour, color and shape analysis beyond the striate cortex.

The corticocortical pathway from striate cortex into the temporal lobe plays a crucial role in the visual recognition of objects. Anatomical studies indicate that this pathway is mainly organized as a serial hierarchy of multiple visual areas, including V1, V2, V3, V4, and inferior temporal cortex (IT). As expected from the anatomy, we have found that neurons in V4 and IT, like those in V1 and V2, are sensitive to many kinds of information relevant to object recognition. In the spatial domain, many V4 cells exhibit length, width, orientation, direction of motion and spatial frequency selectivity. In the spectral domain, many V4 cells are also tuned to wavelength. Thus, V4 is not specialized to analyze one particular attribute of a visual stimulus; rather, V4 appears to process both spatial and spectral information in parallel. A special contribution of V4 neurons to visual processing may lie in specific spatial and spectral interactions between their small excitatory receptive fields and large silent suppressive surrounds. Thus, although the excitatory receptive fields of V4 neurons are small, the responses of V4 neurons are influenced by stimuli throughout a much larger portion of the visual field. In IT, neurons also appear to process both spatial and spectral information throughout a large portion of the visual field. However, unlike V4 neurons, the excitatory receptive fields of IT neurons are very large. Many IT neurons, for example, are selective for the overall shape, color, or texture of a stimulus, anywhere within the central visual field. Together, these results suggest that within the areas of the occipito-temporal pathway, many different stimulus qualities are processed in parallel, but the type of analysis may become more global at each stage of processing.

Animals↗
PubMed1993

Benefit from visual cues in auditory-visual speech recognition by middle-aged and elderly persons.

The benefit derived from visual cues in auditory-visual speech recognition and patterns of auditory and visual consonant confusions were compared for 20 middle-aged and 20 elderly men who were moderately to severely hearing impaired. Consonant-vowel nonsense syllables and CID sentences were presented to the subjects under auditory-only, visual-only, and auditory-visual test conditions. Benefit was defined as the difference between the scores in the auditory-only and auditory-visual conditions. The results revealed that the middle-aged and elderly subjects obtained similar benefit from visual cues in auditory-visual speech recognition. Further, patterns of consonant confusions were similar for the two groups.

Acoustic Stimulation↗
PubMed1996

The recognition potential and conscious awareness.

The idea that conscious awareness of a recognizable image is necessary for it to evoke the recognition potential (RP) was tested by asking bilingual subjects to selectively attend to superimposed English and Chinese word images. The subjects detected most of the words in the attended language, but were largely oblivious of words in the non-attended language. Attended word images evoked the RP. Non-attended words did not. RP latency was less for Chinese than for English words. This provided a basis for inferring which language a subject was trying to read when valid English and Chinese words were both present. A subject was looking for Chinese if the latency was short and for English if it was long. The results showed that selective attention had a powerful effect on the RP. They supported the idea that conscious awareness is necessary for evoking it, though they did not rule out the theoretical possibility that some method not yet tested could be found that would block conscious awareness without blocking the RP. The sensitivity of the RP to what a subject is trying to see and its low variance seem to provide advantages for studying visual perception. It provides a short latency indicator of image processing that merits further investigation. Use of it may lead to a better understanding of visual perceptual processes.

Adult↗
PubMed1985

Visual evoked response abnormality in myoclonus epilepsy with large pupils. Occurrence in a family with acorpuscular myoclonus epilepsy.

Flash and pattern evoked responses were recorded from three siblings with myoclonus epilepsy who all had strikingly large pupils in daylight. Comparison with the visual evoked responses (VERs) of 15 normal and eight epileptic control subjects (including one with myoclonus epilepsy but normal pupils) disclosed a substantial reduction of the amplitude of the flash response as compared with the normal pattern response in these three patients. It is suggested that the VER constellation and the pupillary abnormality, together with the normal electroretinogram and diffusely distributed relative scotomas, were due to a ganglion cell loss in the retina.

Adult↗