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PubMed1991

[VECP (pattern threshold, amplitude, latency) in different light levels. A comparison between healthy eyes, organic and functional amblyopia eyes].

According to Bjerrum [5] and Ammann [2], light attenuation decreases visual acuity at different rates in normals, organic and functional amblyopes. In 27 normal subjects, 19 patients with central fixating squint amblyopia and 12 with organically poor vision, we determined the visually evoked cortical potential (VECP) threshold check size, P100 latency and P2 amplitude for reversing checkerboards of variable size at different levels of luminance. After light attenuation, we found a different rate of change for VECP threshold check size in normal subjects and patients with squint amblyopia, which lessened after the fovea was occluded. With suprathreshold checks, normal subjects and patients with squint amblyopia exhibited significantly smaller amplitude/latency changes after light attenuation than patients with organically poor vision. Only patients with squint amblyopia exhibiting a visual acuity of greater than 0.2 showed smaller VECP changes than normal subjects during light attenuation. According to these findings, the different rate of change in visual acuity after light attenuation in normal subjects and patients with squint amblyopia is locus specific [7] rather than luminance specific [12, 13]. We conclude that cortical disinhibition of the parafoveal retina [20] is responsible for the preservation of visual acuity in squint amblyopia during light attenuation.

Adolescent↗
PubMed1991

Visual-evoked response binocular summation in normal and strabismic infants. Defining the critical period.

Pattern visual-evoked response binocular summation (VERBS) was recorded in normal infants, between the ages of 1-58 months, and in similar-aged esotropic infants before and at various times after corrective surgery. The normal subjects had no significant VERBS at 1.5 months of age, developed a rapid acceleration of VERBS between 1.5-3 months, and then gradually declined in VERBS from 3-58 months. The peak of the VERBS by age function at 3 months was well in the facilitation range (greater than 2.0) and corresponded to the general age range for the onset of binocular eye alignment, fusion, and stereopsis. The results from the early-onset esotropic patients revealed a similar function to that found in normal subjects; however, the function was triggered by surgical eye alignment. The peak of the VERBS function for esotropic subjects was lower than normal, and the initial rise was less rapid. It is proposed that the VERBS function reflects the human critical period for the development of binocular vision. In this framework, data from both infant developmental studies and adult studies were clarified.

Adolescent↗
PubMed1983

On the possible role of temporal delays of afferent processing in Parkinson's disease.

Visual evoked potential (VEP) latency is one measure of afferent delays in Parkinson's disease. New aspects of temporal processing were studied in the VEP of 7 patients and 10 normals. For this analysis the patterned stimulus was simultaneously modulated at two temporal frequencies. Phase shifts of non-linear VEP components in patients, compared to normals, revealed that an abnormality of temporal processing in this disease must be caused by altered neuronal interactions, not only by simple conduction defects.

Adult↗
PubMed1983

Flash and pattern VEPs: examples of cases of hysterical amblyopia and provoked visual impairment (Uhthoff's sign).

The diagnostic application of averaged visual evoked potentials (VEPs) is illustrated in the investigation of hysterical amblyopia and multiple sclerosis. Averaged VEPs elicited either by a flash of light or a presentation of a grating lasting 100 ms were recorded from the occiput of patients. All the VEPs in hysterical amblyopia were normal. In multiple sclerosis the flash VEPs looked normal for both eyes, whereas the VEPs elicited by grating (2 and 5 c/deg) showed an increase in the latency of the first positive wave, again for both eyes. After physical exercise the VEPs from the right eye were dramatically reduced in amplitude (Uhthoff's sign).

Adolescent↗
PubMed1993

Visual evoked response asymmetry only in the albino member of a family with congenital nystagmus.

PURPOSE: To examine the purported relationship between visual fiber misrouting and congenital nystagmus (CN) by studying a family containing members with either hereditary CN alone or in conjunction with albinism. METHODS: Eight relatives in three generations of a family with two genetic disorders (congenital nystagmus [CN] and albinism) underwent complete ophthalmologic examination and visual evoked potential (VEP) assessment of visual pathway organization using a luminance flash and checkerboard pattern onset/offset stimulus paradigm. Age-matched controls patients (albino, CN, or normal) corresponding to the three affected family members underwent the same procedure. RESULTS: The standard VEP albino misrouting test did not reveal any signs of abnormality in all family members tested except for the clinically diagnosed 8-month-old albino proband patient. Visual evoked potential assessment from the albino patient evinced contralateral asymmetry characteristic of aberrant temporal retinostriate projections. CONCLUSIONS: Although CN and albinism share some of the same clinical symptoms, these findings indicate that the disorders may be inherited and manifested independently in members of one family. Furthermore, the functional and/or structural factors responsible for CN cannot be readily ascribed to VEP retinal-cortical misprojections recorded in albinism.

Adult↗
PubMed1997

Visual evoked potentials in primary hypertension.

Functional integrity of sensory pathways in the brain has not been well documented in hypertension. It is suggested that vascular endothelial changes including hyalinisation during hypertension may lead to demyelination in the vulnerable areas of the brain. Since optic nerve is considered to be part of brain hence the present study was done to find out if visual pathways are involved in hypertension. Transient pattern reversal visual evoked potentials (VEPs) from 01, 02 scalp regions were recorded in 23 primary hypertensive patients and compared with 14 normotensive control. Of these, six patients showed delayed P1 latencies beyond 99% tolerance limit i.e. Mean + 3 SD of normal. The remaining 17 had latencies of all positive (P1-P3) and negative (N1-N3) waves comparable to those of the control group. Correlation Coefficient worked out, showed significant correlation between systolic BP and P1 latency in the control group only. No other parameter showed any correlation with P1 latency & amplitude in both the groups. These findings show that fluctuations of BP in normotensive subjects have correlation with P1 latency. This correlation ceased to exist in hypertensive patients and abnormality in P1 latency of VEP was detected in 26% cases.

Adult↗
PubMed2004

Anteromedial temporal cortex supports fine-grained differentiation among objects.

Patients with damage to left anteromedial temporal cortex often show a striking deficit: they fail to recognize animals and other living things. This failure of recognition presents an important challenge to theories of the neural representation of conceptual knowledge. Here we propose that this lesion-behaviour association arises because polymodal neurons in anteromedial temporal cortex integrate simple features into complex feature conjunctions, providing the neural infrastructure for differentiating among objects.

Adult↗
PubMed1978

[A developmental study of visual-motor function in cerebral palsied children (author's transl)].

The purpose of this study was to investigate whether the disorder in the visual-motor function of cerebral palsied children was affected by specific defects or by the distortion in perceptual motor system or by mere developmental lag in the function of recognition and reconstruction using the method of multiple choice and Shochi's Block Design Test (1971). The results were as follows : Cerebral palsied children's developmental lag in the function of recognition was not conspicuous but the development in the function of reconstruction was obviously inferior to that of normal children. There was the difference in reconstruction ability by children with the types of cerebral palsy and intellectual levels and design-constructive patterns. Those factors and the developmental lag cause visual-motor disorders.

Cerebral Palsy↗
PubMed2006

Age of acquisition affects object recognition: evidence from visual duration thresholds.

The impact of age of acquisition (AoA) on object recognition was explored in three experiments measuring visual duration threshold (VDT) for the identification of pictures labelled with early and late acquired names. Participants viewed briefly displayed images preceded and followed by a pattern mask. The minimum display duration required for correct identification was shorter for pictures labelled with early names than for those labelled with late names. In Experiments 2 and 3 we explored the effects of two forms of visual degradation on VDT for pictures with early and late acquired names. Both degradation by superimposed visual elements, and degradation by contrast reduction extended VDT, but only the former interacted with AoA. We conclude that both AoA and degradation by superimposed visual elements affect the efficiency of visual object recognition, but only degradation by contrast and not AoA affects the efficiency of earlier pre-recognition processes.

Analysis of Variance↗
PubMed1995

Event-related brain potentials differentiate priming and recognition to familiar and unfamiliar faces.

Recent studies from our laboratory have resulted in the identification of an event-related potential (ERP) correlate of a visual memory process. This memory process is reflected by a reduction in the voltage of the visual memory potential (VMP) to repeated pictures of unfamiliar faces compared to novel pictures of faces. In the current experiment we used unfamiliar and famous faces in an identical repetition priming paradigm, while the subject differentially recognized famous from non-famous faces. Significant differences in response times were obtained between primed and unprimed familiar faces, but not between primed and unprimed unfamiliar faces. The VMP was reduced to primed unfamiliar faces and significantly diminished to primed familiar faces compared to unprimed stimuli. Priming was typically reflected by a reduction of the VMP at the occipito-temporal region, whereas recognition resulted in a diminution of the VMP at both the occipito-temporal region and at the frontal region. These data support the involvement of differential neural systems for priming and recognition of visual stimuli.

Adult↗
PubMed1993

A neurophysiologic correlate of visual short-term memory in humans.

Neurophysiological investigations in non-human primates and neuropsychological studies in patients with lesions indicate that the inferotemporal cortex is critically involved in visual object recognition. We have recorded event-related potentials from 31 electrodes in a group of healthy normal individuals performing a modified delayed matching to sample task. We have identified a visual memory potential (VMP) which indexes visual short-term memory in humans. This component of the event-related brain potential occurs as early as 170 msec, is maximal at 240 msec, and is generally located in the temporal region. Both the temporal and spatial characteristics of the VMP in humans are in keeping with single cell studies in monkeys.

Adult↗
PubMed2007

[Neural mechanisms for object and color recognition].

We reported double-dissociation between the visual processing of the edges and the surfaces of objects. Patients with lateral occipital damage showed selective impairment in the perception of edges whereas those with medial ventral occipital damage showed selective impairment in the perception of the 3D structure of the surface. Patients with medial ventral occipital damage also exhibited impaired perception of color, which is also a surface property. Those results were consistent with those from neuroimaging studies. Taken together, those studies suggest that objects may be processed in two separate pathways in the ventral occipital cortex: the edges of objects are processed in the lateral pathway and the surface of objects are processed in the medial pathway. Both edges and surfaces play important roles in object recognition, and both types of perception should be evaluated in patients with visual agnosia.

Cerebral Infarction↗
PubMed1993

Influence of visual guidance on braille recognition: low lighting also helps touch.

This study was an attempt to clarify the mechanisms responsible for the benefits of visual guidance in tactual braille recognition. Subjects touched +90 degrees tilted braille under normal room lighting, or with low lighting, with or without visual guidance. Both visual information about finger angle and spatial reference information were manipulated with stained glass and light-emitting diodes. The provision of visual information about finger angle alone was no help to braille recognition, and performance was low. Adding visual spatial reference information to vision of finger angle raised performance. However, recognition accuracy was also substantially improved by low lighting. The benefits of darkness for haptics did not generalize to the reading of upright, two-letter braille words. It was proposed that extraneous visual information may distract sighted subjects in haptic tasks that require mental rotation of visual images.

Adolescent↗