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PubMed2003

Clinical value of the Beery visual-motor integration supplemental tests of visual perception and motor coordination.

PURPOSE: Children may perform poorly on a test of visual-motor integration due to deficits in one or more of the following: visual analysis/visual spatial ability, motor coordination, visual conceptualization, or visual-motor integration. The VMI Supplemental Developmental Test of Visual Perception (VP) and VMI Supplemental Developmental Test of Motor Coordination (MC) were developed to help differentiate between such difficulties after administration of the Beery-Buktenica Developmental Test of Visual-Motor Integration (VMI). However, the clinical value of the VMI supplemental tests has not been reported. METHOD: The VMI, VP, and MC were administered to 193 children (mean age = 8.77 years). RESULTS: Multiple linear regression revealed that the supplemental tests were significantly related to the VMI (VP: beta = 0.212 +/- 0.044, p < 0.001; MC: beta = 0.422 +/- 0.299, p < 0.001) but explained only 36.2% of the variance in the VMI. Poor performance was defined as a score >1 SD below the mean for study population norms and below the 16th percentile for published norms. Using study population norms, 35 children did poorly on the VMI, 20% of whom scored poorly on VP, 14.3% of whom scored poorly on MC, 17.1% of whom scored poorly on both supplemental tests, and 48.6% of whom scored within normal on both supplemental tests. Using the published norms, 40 children scored poorly on the VMI. Twenty-eight children scored poorly on VP, 39% of whom scored within normal on the VMI. Fifty-six children scored poorly on MC, 54% of whom scored within normal on the VMI. CONCLUSION: There was a significant amount of variance in performance on the VMI that was not explained by performance on the tests of VP or MC alone. Each area should be individually assessed during the visual perceptual examination of children, regardless of performance on the VMI. Even children who perform within normal limits on the VMI may show a deficit in VP or MC.

Child↗
PubMed2000

Spatial distribution of contextual interactions in primary visual cortex and in visual perception.

To examine the role of primary visual cortex in visuospatial integration, we studied the spatial arrangement of contextual interactions in the response properties of neurons in primary visual cortex of alert monkeys and in human perception. We found a spatial segregation of opposing contextual interactions. At the level of cortical neurons, excitatory interactions were located along the ends of receptive fields, while inhibitory interactions were strongest along the orthogonal axis. Parallel psychophysical studies in human observers showed opposing contextual interactions surrounding a target line with a similar spatial distribution. The results suggest that V1 neurons can participate in multiple perceptual processes via spatially segregated and functionally distinct components of their receptive fields.

Animals↗
PubMed1996

Timing of fiber arrival and dennervation of postsynaptic neurons is required for restoration of visual perception by regenerating axons.

Axotomized CNS neurons, whose regenerating axons are guided to their natural target areas in the brain with the aid of peripheral nerve grafts, are capable of establishing synaptic contacts with normal morphological and electrophysiological properties. The present study was undertaken to analyse the functional significance of the reestablished synaptic contacts made by these regenerated retinofugal neurons. Adult rats were trained in a T-maze to obtain a food reward with the aid of visual cues. One of their optic nerves was transected and the regenerating axons were guided into the optic tract with a peripheral nerve graft, in order to enable them to reinnervate the superior colliculus (SC) and thalamus. Postoperative testing of the animals showed a drastic improvement of visual perception. The protocol of dennervation of the SC (prior to, simultaneous or with a delay with respect to fiber arrival) determined the performance of the animals. Rats belonging to the first two groups performed almost as well as they did prior to the transplantation. The functional integrity of the retina was assessed by electroretinography (ERG) which revealed typical rod spectral sensitivity at 380 and 500 nm, but reduced responsiveness to illumination. In accordance, neuroanatomical assessment of the retinal ganglion cells revealed that about 15% of the axotomized neurons contributed to regeneration of axons. These findings show that a restricted population of retinofugal axons of capable of restoring higher visual functions such as light-discrimination-behaviour in the adult rat. Prerequisites for the restoration of visual perception are first the preservation of the intraretinal integrity, and second the temporal matching of fiber arrival and dennervation of postsynaptic neurons.

Animals↗
PubMedDate not supplied

Some neurophysiological correlates of visual perception.

A study was made of the structural organization of simple and complex receptive fields of the visual cortex. The bidimensional weight function of the field that determines its basic properties as a filter of spatial frequencies (spatial-frequency and orientational sensitivity) was investigated. Two types of modules-cylinders of the cortical neurons, the receptive fields of which are directed toward a single area of the visual field, and adapted to different spatial frequencies and orientations, are discussed. One type contains neurons, the receptive fields of which describe amplitude and phase of the visual signal and give Fourier descriptions of a part of the image; in the second type, the receptive fields describe only the amplitude and give the power spectrum. A comparison with psychophysical data indicates that the second type serves to describe texture. Inhibition in the receptive fields induced by frequencies lateral with respect to the optimal frequency and orientation perpendicular to optimal orientation points to the mutually inhibiting effects between neurons of the module. The significance of such an organization for visual perception is discussed.

Animals↗
PubMed2003

Attentional dynamics and visual perception: mechanisms of spatial disorientation in Alzheimer's disease.

Visuospatial disorientation forces Alzheimer's disease patients to abandon independent activities. We found previously that limitations of ambulatory and vehicular navigation are linked to impaired visual motion processing in Alzheimer's disease. We now hypothesize that these perceptual impairments reflect temporal constraints on visual attention. We evaluated attentional, perceptual and neuropsychological capacities in 14 Alzheimer's disease patients and 12 age-matched older normal controls. The temporal dynamics of visual attention were measured using rapid serial visual presentation (RSVP) to assess the attentional blink. Visual processing for spatial orientation was assessed using perceptual thresholds for optic flow, the visual motion seen during observer self-movement. Alzheimer's disease patients show an exaggerated attentional blink during RSVP, identifying the first of two targets but missing the second target depending on the number of intervening distractors. They also show a unique form of attentional masking in which they miss the first target but identify the second, again depending on the number of intervening distractors. Both types of RSVP errors are correlated with selectively elevated optic flow thresholds in Alzheimer's disease patients. This suggests that temporal constraints on visual perception might impair optic flow analysis and contribute to spatial disorientation in Alzheimer's disease. These findings are consistent with two-stage models of visual perception, suggesting that the working memory mechanisms in the second stage provide feedback control of input to category-specific perceptual processors in the first stage.

Aged↗
PubMed1992

Solving the "real" mysteries of visual perception: the world as an outside memory.

Visual science is currently a highly active domain, with much progress being made in fields such as colour vision, stereo vision, perception of brightness and contrast, visual illusions, etc. But the "real" mystery of visual perception remains comparatively unfathomed, or at least relegated to philosophical status: Why it is that we can see so well with what is apparently such a badly constructed visual apparatus? In this paper I will discuss several defects of vision and the classical theories of how they are overcome. I will criticize these theories and suggest an alternative approach, in which the outside world is considered as a kind of external memory store which can be accessed instantaneously by casting one's eyes (or one's attention) to some location. The feeling of the presence and extreme richness of the visual world is, under this view, a kind of illusion, created by the immediate availability of the information in this external store.

Attention↗
PubMed1994

Visual perception. Knowing is seeing.

New visual illusions provide further evidence for the influence of higher-order analyses of the visual scene on the perceived brightnesses of surfaces within that scene.

Contrast Sensitivity↗
PubMed1978

[Piecewise Fourier analysis of images and the role of the occipital, temporal and parietal cortex in visual perception].

On the basis of previously published data, a neuronal scheme of organization of the visual perception in the cerebral cortex, is suggested. An idea of neuronal module is introduced: a cylinder of cortical neurons whose receptive fields are directed towards the same area of the visual field and respond to different spatial frequencies and orientations. A system of overlapping modules is able of piece--wise Fourier--description of portions of the image. The modules of the Clare--Bishop area are composed of receptive fields of different size. Owing to that each neuron of the module projects inhibitory influence upon other neurons, the module acts as a filter picking out the texture. Therefore, the modules of the Clare--Bishop area single out and supply Fourier--description of subimages, the latters being characterized by the same local spectrum within their own limits. The lower portiön of temporal cortex performs a rough identification of subimages and images with the aid of systems of learning neurons. The parietal cortex conforms the description from temporal cortex to the complete description in the modules of occipital cortex, thus performing the transition from an image to a concrete picture.

Animals↗
PubMed1990

Perspectival appearing and Gibson's theory of visual perception.

Although Gibson (1979) did not explicitly discuss the perspectival appearing of the ecological environment, his important ecological approach to visual perception can accommodate both (a) the stream of visual-perceptual experience that flows at the heart of the visual system's total activity of ordinary visual preceiving (ordinary seeing), and (b) the dimension of the visual experiential stream that is the ecological environment's perspectival appearing to the visual perceiver. In the present article, perspectival appearing is located at the level of brain centers of the visual system, where processes are determined by the spatiotemporally structured visual stimulus flux. And the stream of visual experience is interpreted as itself possessing a kind of perspective structure (as does the visual stimulus flux), including variant and invariant features that the visual system isolates and extracts from experience, producing the perceiver's cognitive visual "awareness-of" (Gibson, 1979) the environment and self in the environment.

Attention↗
PubMed2006

Sequential resolution of fragmented visual percepts: experimental investigation of a subject's perceptual experience after a right medial temporal stroke.

This report concerns the fragmented visual percepts in a woman, TR, following a right entorhinal-perirhinal infarct. In a previous report, Weddell [Weddell, R. A. (2005). A visual disorder producing highly selective deletion of recurring letters. Cortex, 41, 471-485] linked TR's highly selective tendency to delete recurrent letters with her fragmented percepts. The conflation of same-identity form elements was attributed to anterior extrastriate damage, which reduced the amount of information sustainable in fully resolved visual percepts, and the present experimental investigation of her subjective account of segment formation and resolution completes the story. She said that complex objects and long words first appeared as blurred regions, which sometimes included form elements. It is argued that figure-centred attentional mechanisms subdivided this blurred region into up to 3-4 parts. String length, lexical status (word vs. nonword), and background colour and/or luminance determined fragment length. Two rules described the fragment resolution sequence: largest segments usually resolved first, left-to-right resolution accounting for a few sequences. This resolution sequence occurred when stimuli were exposed too briefly for saccadic exploration, implicating endogenous attentional shifts. Experiment 4 confirmed TR's assertion that spatial, orthographic, and phonological information were stored during the fragment resolution process. Moreover, TR exerted considerable voluntarily control over the fragment resolution sequence and some influence over fragment length. Finally, these findings were interpreted in terms of an extended version of a neural network model of vision largely derived from nonhuman primate studies.

Adult↗
PubMed2003

Early modulation of visual perception by emotional arousal: evidence from steady-state visual evoked brain potentials.

Allocation of processing resources to emotional picture stimuli was examined using steady-state visual evoked brain potentials (ssVEPs). Participants viewed a set of 60 colored affective pictures from the International Affective Picture System, presented in a flickering mode at 10 Hz in order to elicit ssVEPs. Phase and amplitude of the 10-Hz ssVEP were examined for six picture categories: threat and mutilation (unpleasant), families and erotica (pleasant), and household objects and persons (neutral). Self-reported affective arousal and hedonic valence of the picture stimuli were assessed by means of subjective ratings. Viewing affectively arousing (unpleasant and pleasant) pictures was associated with enhanced ssVEP amplitude at parieto-occipital recording sites, as compared with neutral stimuli. Phase information suggested increased coactivation of right occipitotemporal and frontotemporal sources during processing of affectively arousing stimuli. These findings are consistent with reentrant modulation of early visual processing by distributed networks including subcortical and neocortical structures according to a stimulus's motivational relevance.

Adult↗
PubMedDate not supplied

[Neurophysiologic mechanisms of the change in visual perception in children between 3 and 7 years of age].

Analysis of evoked potentials (EP) to visual images (a homogenous square, a checker-board and a schematic image of a face) has revealed one and the same type EP configuration and reactivity in the projection and posterior associative areas in three to four year old children. Six to seven year old children have exhibited a specialization of cortical areas involvement in the analysis of visual stimuli of different complexity, as manifested in the predominant reactivity of the projection and anterocentral areas in response to presentiation of the checker-board and of the temporo-parieto-occipital zone in response to the face image. Characteristics of involvement of different areas in the analysis of visual stimuli are compared with reaction time and the "time of central processing" in the course of elaboration of a reaction of choice of images out of various number of alternatives. The dynamics of such characteristics in three to four and six to seven year old children is the same in the choice of easily recognizable checker-board and familiar (face) images and does not coincide at the presentation of probabilistic textures: their differentation is readily achieved only by children of senior age. It is assumed that the nature of involvement of different areas in the reaction to complex visual stimuli accounts for the characteristics of visual perception at different stages of individual development.

Age Factors↗
PubMed1990

Use of subjective information in scientific psychology: III. The internal image during visual perception: an introspectionist analysis.

On the basis of personal observation, the writer describes certain characteristics of hypnopompic visual imagery that lead to an understanding of how the internal visual image is experienced. This understanding helps us to see how an internal two-dimensional visual perceptual image could be experienced as an external environment positioned around the observer. The writer suggests how the three-dimensionalized perceptual image is constructed, how it gives the effect of directional looking within the context of seeing widely, and how certain features of visual perception can best be accounted for by the mediation of perception by an internal image.

Attention↗
PubMed1988

Visual perception in high-speed low-altitude flight.

An ongoing exploratory development program on visual perception and control in high-speed low-altitude flight is being conducted by the Human Engineering Division of the Armstrong Aerospace Medical Research Laboratory. This paper begins with a discussion of the necessity of vision for low-altitude flight; proceeds to an analysis of objectives, strategies, and issues in designing a comprehensive research program; presents an overview of several experiments in support of the effort; and ends with a discussion of perceptual information. One of the simulator experiments involves the use of a non-mimetic task, flying at a zero altitude in the presence of strong gusts, in an effort to maximize adaptation to the low-altitude environment. Implications for simulator use are discussed.

Adaptation, Physiological↗