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PubMed1993

A hierarchical model for evaluation and treatment of visual perceptual dysfunction in adult acquired brain injury, Part 2.

A framework for evaluation and treatment of visual perceptual dysfunction in adults with acquired brain injury is presented. The framework is based on the concept of a hierarchical structure of perceptual skill levels that interact and subserve one another. Higher level skills in the structure evolve from the integration of lower level skills and are subsequently affected by disruption of the lower level skills. Oculomotor control, the visual fields, and visual acuity form the foundation skills in the framework, followed by visual attention, scanning, pattern recognition, memory, and visual cognition. The order of evaluation and treatment is dictated by the framework. Emphasis is placed on identification and remediation of deficits in the lower level skills that will cause spontaneous improvement of higher level skills. Three treatment principles and five training guidelines are presented that reflect this concept. Specific examples of treatment tasks are provided.

Adult↗
PubMed2003

A functional gamma-band defined by stimulus-dependent synchronization in area 18 of awake behaving cats.

During the past decade, numerous studies have demonstrated stimulus-specific synchronization of neuronal activity in the gamma-frequency range. However, it appears that the different analyses are based on widely different assumptions about which frequency range to investigate. Therefore, the term "gamma-synchronization" refers to an inhomogeneous spectrum of definitions and corresponding frequency bands. Moreover, most studies have been performed in anesthetized animals or in awake animals by use of fixation paradigms. Thus, it is difficult to relate these results to alert animals behaving under natural conditions. Here, we investigate stimulus specific synchronization in primary visual cortex of awake cats in a tracking paradigm. We record local field potentials and multiunit activity simultaneously from multiple electrodes. (1) We demonstrate that visual stimulation induces neuronal synchronization in a broad frequency range reaching well above 100 Hz. (2) We derive a functional gamma-band based on an objective criterion: We show that synchronization of neuronal activity is optimally orientation-tuned when a broad frequency band is considered. This band starts above 40 Hz, a frequency that is typically related to the term gamma-synchronization, and extends to very high frequencies. Interestingly, the frequency of maximum synchronization is different from the frequency at which synchronization is most stimulus specific. (3) We demonstrate synchronization of neuronal activity in a distinct low-frequency band with different properties suggesting separate functional roles of low- and high-frequency synchronization.

Animals↗
PubMed1987

Visual acuity prediction using the visual evoked response.

A technique is described for predicting visual acuity in adult humans by using the visually evoked response (VER). This involves using a pattern-reversal checkerboard with a small check size (5.5. min arc) as the stimulus, and measuring the peak-to-trough amplitude of the VER wave arising from it. The technique is therefore both rapid and convenient. The pattern-reversal rate was varied in order to assess the influence of the temporal modulation on the VER waves. The results suggest that a rapid pattern reversal rate produces a VER which displays a reduced association with spatial processing.

Adult↗
PubMed1986

Patterns of stimulus- and self-induced slow brain potentials--a sign of task-specific preparation.

Does the scalp distribution of slow shifts in human brain potentials depend upon the processing demands? The question was approached applying two different paradigms. In the first study, the anticipation of haptic tasks presented to either of the hands was found to give rise to a contralateral slow negative brain potential (SP). The second study demonstrated that comparable hemisphere-specific patterns can be self-induced by means of biofeedback training. These results suggest that negative SPs (like the CNV) indicate preactivation of those brain-regions that process the expected task.

Biofeedback, Psychology↗
PubMed1985

Comparison of pattern VEPs and preferential-looking behavior in 3-month-old infants.

Studies of visual acuity in human infants between 1 and 6 months of age using the visual-evoked potential (VEP) and forced-choice preferential looking (FPL) have shown that acuity is one to two octaves higher by VEP estimates than by FPL estimates. In an attempt to study these differences, the authors obtained both VEP and FPL data from 26 3-month-old infants. VEP data were obtained with gratings of 0.31, 0.62, 1.25 and 2.50 cycles/deg, which were counterphase alternated at 2 Hz. FPL data were obtained for stationary gratings using either the method of constant stimuli or a staircase procedure. Our study revealed three major findings: (1) recordable VEPs can be obtained for spatial patterns that are below threshold by behavioral measures; (2) the use of different scoring criteria that yields comparable VEP and FPL group mean acuities does not yield a significant correlation between VEP amplitude acuity and FPL acuity for individual infants, probably because of the inherent "noise" in each technique; and (3) when VEP latency rather than amplitude is used to estimate acuity, there is a significant correlation between electrophysiology and behavior.

Discrimination, Psychological↗
PubMed1982

Visually evoked potentials to pattern stimuli in cortex of binocularly deprived cats.

Visually evoked potentials (VEPs) were compared in 7 normally reared cats (N cats) and 9 cats deprived of pattern vision during postnatal period. In 4 deprived cats (D cats) recording was done immediately after deprivation period which lasted from 6 to 24 months. In 5 cats (DE cats) 6 months of deprivation was followed by 4-18 months of visual experience. Two stimuli were used: a large stationary stimulus (a 30 per 30 degrees grating pattern illuminated by flash) and a small moving stimulus (a smaller grating pattern was located in different parts of visual field and illuminated by a moving 1 per 4 degrees light slit). The VEPs were recorded in the marginal, suprasylvian, ectosylvian and sigmoid gyri. As compared with N cats, in D cats the VEPs in all cortical areas were of simpler form, more variable and of greater amplitude. Moreover, in contrast to N cats, in D cats the VEPs were of similar amplitude when evoked from the contra or homolateral visual field. However, results in DE cats showed that these changes are largely reversible.

Animals↗
PubMed1994

[Visual information processing in humans].

Recent advances in parallel information processing of primates and humans have been reviewed. First, I review what is known about physiology and anatomy of the primate visual pathways. Several lines of evidence suggest that the primate visual system consists of the parvocellular (P) and the magnocellular (M) pathways. M-system originates from the A retinal ganglion cells that project to the visual cortex (V1) via the magnocellular layers of the lateral geniculate nucleus (LGN). This system plays an important role for motion and stereopsis. P-system derives from the B retinal ganglion cells that project to V1 via the parvocellular layers of the LGN. This system shows selectivity for color vision and form perception. Second, I focus on the information processing of the human visual pathways. Psychophysical evidence suggests that there are also P and M systems in humans. However, there have been few electrophysiological studies which intend to separate the responses specific to P and M systems in human visual evoked potentials (VEPs). Based on the physiological distinctions between P and M systems, the use of isoluminant color patterns and apparent motion display allows us to evaluate P and M systems, respectively.

Animals↗
PubMed1985

Localization of cortical activity associated with visual recognition in humans.

The Laplacian analysis described previously is used to localize cortical activity subserving visual object recognition in humans. In the first of two experiments, subjects are shown pictures of a human face corrupted by varying amounts of noise. After each picture has been presented for 34 ms against a large uniformly illuminated background, the subject is required to report whether or not he saw the face, by pressing a button. The Laplacian response associated with the report that the face is seen differs from that associated with the report that the face is not seen. The difference between these two Laplacian responses has a simple wave form with peak activity at approximately 206 ms after stimulus onset and approximately 196 ms before median reaction time for the button-press report. Its amplitude and polarity, which vary with centre-electrode location over the posterior scalp, are used to construct a map showing the location of cortical activity subserving recognition of the face. This cortical activity localizes to both temporal lobes with some degree of right hemispheric lateralization in right-handed subjects. In the second of the two experiments, subjects are shown the silhouette of a simple shape, such as a triangle, embedded in a large random dot field. Each silhouette is presented for 17 ms. The visibility of the shape is made to vary from trial to trial and the subject is required to report for each trial whether or not the shape is seen. The Laplacian response associated with the report that no shape is seen is very much smaller than that correctly identifying the shape. The difference between these two Laplacian responses has a simple wave form with peak activity at approximately 207 ms after stimulus onset. Its wave form is essentially the same as that associated with face recognition. Its amplitude and polarity, which vary with centre-electrode location over the posterior scalp, are used to construct a map showing the location of cortical activity subserving recognition of the simple shape. This cortical activity localizes to both temporal lobes with strong right hemispheric lateralization in right-handed subjects. The general topography of this activity is similar to that subserving face recognition. Although generally similar, there are measurable differences between the topographies of right temporal lobe activity associated with face recognition and that associated with simple shape recognition.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain Mapping↗
PubMed1975

Stimulus complexity, EEG abundance gradients, and detection efficiency in a visual recognition task.

Occipital EEG was monitored while subjects inspected 27 projected patterns. The number (N) and variety (V) of elements in the patterns were varied systematically. There were three levels of N (6, 12 or 24 elements) and three levels of V (circles, squares or hexagons occupying all, one half or one third of the element locations for all levels of N). Subjects were instructed that they would be required in a post-test to recognize the patterns, among patterns which had not appeared; they were also informed that the patterns had been constructed according to a set of simple rules, but the nature of these rules was not made fully explicit. The EEG was quantified by means of low-frequency analysis, yielding measures of abundance (theta, alpha and beta) and mean dominant frequency. For the recognition task, nine stimulus items were embedded among 45 items. Recognition efficiency was measured by means of the signal detection theory discrimination index (d'). The results were as follows: (i) Both N and V were inversely related to alpha abundance (P less than 0-01); (ii) the strongest relationship between stimulus parameters and the EEG held for N and EEG beta activity (13-5-19-5 Hz;P less than 0-001), where again the EEG and N were inversely related; (iii) there was a significant (P less than 0-05) direct relationship between N and theta activity; (iv) contrary to prediction, mean dominant alpha frequency decreased as N increased; (v) d' correlated significantly with a number of effects for N, i.e. subjects who exhibited greatest EEG discriminability of items during exposure of the patterns, subsequently obtained the higher detection scores in the recognition task. The work described therefore demonstrates that only only do stimulus parameters have systematic effects upon brain activity as measured by the EEG, but that such effects have functional value and reflect aspects of efficiency. The results are fully compatible with arousal theory constructs relating physiological reactivity and performance.

Adolescent↗
PubMed1996

Inattention and the perception of visual feature conjunctions.

Visual processing of objects in the absence of focused attention appears to be limited. We varied the degree of attention, or visual processing, that observers paid to objects using an instruction set manipulation. In 2 experiments, subjects performed tasks that required superficial or detailed visual analysis of the objects involved. In subsequent recognition tests, information about conjunctions of shape and internal color/texture pattern was limited when only superficial visual analysis was required to encode the object. This implies that the degree of visual processing, during object encoding affects the likelihood that feature conjunctions are incorporated into the visual representation of these objects.

Adult↗
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↗