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At least 1,261 records · Page 70Linked to original sources

PubMed1975

Laminar thermocoagulation of the visual cortex in the rat. II. Visual pattern discrimination.

Hooded rats were trained on a series of four visual discrimination tasks in a Y-maze, and subjected to a variety of posterior cortical lesions. In 17 animals this consisted of an extensive aspiration lesion contralateral to a more superficial lesion made by laminar thermocoagulation and centered over the striate area. After operation the animals were tested on the same problem series. The behavioral deficit in this group varied with the extent and depth of the thermal lesion, and six animals with very superficial thermal lesions displayed an isolated difficulty in solving an encircled triangle problem. This deficit seemed to be referable to widespread involvement of supragranular cortex, and specifically of layer I of area striata which receives an input from the nonspecific thalamocortical afferents. The possible influence of various interlaminar projections upon underlying vertically-oriented cell columns as a mechanism for the mediation of 'selective attention' was discussed.

Animals↗

PubMed1994

Snellen visual acuity versus pattern reversal visual-evoked response acuity in clinical applications.

We compared the best-corrected Snellen acuity (SA) and the pattern reversal visual-evoked response (PVER) acuity in normal subjects and patients. Forty-two eyes of 42 normal subjects were controls; 457 eyes of 329 patients comprised the patient group. A steady-state stimulus with five check sizes ranging from 160 to 10 min in 1.0-octave steps was used. The PVER acuity was derived from the best-fit linear function relating the amplitude to the log-adjusted check size. Three intercepts of 0, 1 and 2 microV were used in both groups, and the PVER acuities were called P0, P1 and P2. The SAs in normal subjects ranged from 20/15 to 20/20 (mean, 20/18.3) and in patients from 20/15 to 20/1,600 (mean, 20/56.9). In normals, the P0 showed the best agreement with the SA (mean acuity difference, +0.34 octave). The SA and P0 agreed within +/- 2.0 octaves in 33/42 (78.6%) eyes. In patients, the P0 also showed the best agreement with the SA; 306/457 (67.0%) eyes showed an acuity difference within +/- 2.0 octaves. Unlike normals, 83/457 (18.2%) eyes showed an acuity difference > -3.0 octaves. These eyes mostly had optic nerve disease with a flattened PVER amplitude-check size function curve. The P0 seems to correlate better with SA than P1 and P2, but this analytical method may be less effective in the presence of certain pathologic conditions.

Adolescent↗

PubMed1977

Lateral asymmetries in visual perception: a review of tachistoscopic visual half-field studies.

Experiments using the visual half-field paradigm are reviewed with special reference to the three theories which purport to account for perceptual asymmetries: the left-to-right internal scanning mechanism theory, the direct anatomical access theory, and the attentional bias theory. Recent evidence has clearly shown that the direct anatomical access theory can account for virtually all lateral asymmetries in the perception of verbal and spatial stimuli. The results of the studies reviewed strongly support a model of brain function which suggests that the simultaneous processing of verbal and spatial stimuli does not constrict the attention of either hemisphere. The difficulty in separating the factors of hemispheric processing and stimulus characteristics is discussed. It is suggested that a reliable conclusion about the role of the cerebral hemispheres can only be made when a better description of the operating characteristics of the hemispheres is available.

Attention↗

PubMed1993

Visual perceptual differences in the dyslexic reader: evidence of greater visual peripheral sensitivity to color and letter stimuli.

The present study replicated the 1987 work of Geiger and Lettvin and of Grosser and Spafford in 1989 in providing evidence for greater peripheral sensitivity to individual letter and color stimuli for 10 dyslexics as compared to 10 normal readers. Earlier studies have demonstrated that dyslexics tend to favor clearer images in the peripheral retina as compared to the foveal advantage of proficient readers. For letter and color stimuli individually presented there was a statistically significant difference between dyslexics and proficient readers based on the ability of dyslexics to recognize both letter and color stimuli at greater peripheral distances from the point of fixation. This study directly supports the consideration of visual perceptual factors in the identification and discussion of dyslexia.

Adult↗

PubMed1978

[Neurons of the rabbit visual cortex with simple and complex visual fields].

The receptive filelds of orientation-selective neurons were studied in the rabbit visual cortex. Two mechanisms of the selectivity were found: the mutual inhibition between on- and off-regions of the receptive field (simple type) and the orientation-dependent inhibition within the uniform region of the receptive field. The non-selective neurons could exhibit the lateral inhibition within the uniform region of the receptive field also. It is supposed that both "simple" and "complex" cells originate from the non-selective units.

Animals↗

PubMed1984

[Activity of neurons of the somatosensory and visual cortex in the rabbit during visual field testing and performance of food-getting behavior].

The activity of somatosensory and visual cortex neurons was compared in experiments on freely moving rabbits during testing of their receptive field and during natural "stimulation" of the receptive areas by environmental objects in food-acquisition behaviour. It was found that the neuronal activity during the receptive field testing may correspond completely, partly or not at all to that in food-acquisition behaviour, i.e. units displaying a certain relation to a receptive field area during the testing may keep it unaltered, alter it or lose it in food-acquisition behaviour. The different activity in the behaviour was observed even in neurons having identical receptive fields during testing. A conclusion is made that the picture of unit activity in the active goal-directed behaviour being modelled on the basis of receptive field testing may be rather vague. The results of experiments with the receptive field testing may help to develop the concept of processing of information about environment in the behaviour but with some limitations whose formulation demands special investigations.

Animals↗

PubMedDate not supplied

[Dynamics of evoked responses in the visual cortex of intact and callosotomized cats to visual stimuli of different intensity].

The comparison of histograms of distribution of monocular and binocular EPs amplitudes in the striate and parastriate cortex of intact and callosectomized cats with the corresponding histograms of intensities of random light flashes revealed a transformation of stimuli distribution function. In intact animals, EPs distribution was characterized by a left-side asymmetry and predominance of mean-amplitude EPs. It is suggested that the above distribution characteristics reflect the principle of optimization. Its presence as well as characteristics of its manifestation in definite visual areas and with different types of stimuli lateralization are largely due to transcallosal influences modulating the value and power spectrum of thalamocortical excitation.

Animals↗

PubMed1994

[Binocular competitive mechanisms in the visual cortex in early developing kittens of monocular deprivation and reverse suture revealed by pattern visual evoked potential].

Using contrast reversing square- wave gratings as stimuli the pattern visual evoked potentials (P-VEP) and pattern electroretinograms (P-ERG) were simultaneously recorded to determine the spatial frequency tuning curves for kittens of monocular deprivation (from 8th to 12th postnatal week) and reverse suture (from 12th to 15th postnatal week), as compared with those of normal kittens of the same age and adult cats. The results showed that in the range from spatial frequency 0.12 to 1.5 c/d the amplitudes of P-VEP responses driven respectively by the left and the right eyes in normal kittens were similar but clearly smaller than those driven binocularly. For kittens with one eye deprived, the P-VEP amplitudes driven by the deprived eye decreased markedly. In contrast, the P-VEP amplitudes driven by the undeprived eye increased significantly, while the P-VEP amplitudes driven by simultaneous stimulation of both eyes were intermediate between the two monocular responses. For the reversely sutured kittens, the P-VEP amplitudes driven by the formally deprived eye recovered to some extent, while the P-VEP amplitudes driven by the reversely sutured eye decreased, and their amplitudes tended to be quite close. The P-VEP amplitude driven by both eyes was the biggest. Neither such shift of spatial frequency tuning curves of the P-VEP in adult cats, nor such functional competition between the two eye in P-ERG responses during early development of kittens of monocular deprivation and reverse suture was found.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1985

Differences between visually triggered human forearm movements with visual and auditory relevant feedback.

The effects of visual and auditory relevant feedback on human forearm movements elicited by random position signal sequences were examined. Forearm movements were performed with four feedback conditions. We observed the reaction time, the holding time, and the adjustment error sequences when the arm moved briskly and accurately to the target position. As the results, the reaction times for auditory relevant feedback were shorter than those for the others (visual or no feedback). The holding times for auditory relevant feedback were longer than those for the others. And the subjects had about one adjustment error to terminate on the target zone.

Acoustic Stimulation↗

PubMedDate not supplied

Development in severely visually handicapped children and visual therapy remediation.

The motor and cognitive development of a visually handicapped child is delayed due to various constraints placed on learning by the handicap. The child requires a functional visual assessment, and assessment of mental & motor development. Based on these findings a total remediation programme needs to be worked out. This is individualised, integrated & includes stimulation of residual vision, optional use of residual vision and special measures to promote general development.

Adolescent↗

PubMed1975

Biochemical aspects of the visual process. XXVII. Stereospecificity of ocular retinol dehydrogenases and the visual cycle.

A comparative study is made of the stereospecificity of two particulate retinol dehydrogenases from bovine eyes and of horse liver alcohol dehydrogenase. The particulate retinol dehydrogenase of outer segments reacts with the all-trans isomers of retinaldehyde and retinol but not with the 11-cis compounds. In contrast, a particulate retinol dehydrogenase present in pigment epithelium reacts preferentially with the 11-cis compounds. Horse liver alcohol dehydrogenase (EC 1.1.1.1.) can convert both isomers, but the all-trans isomers are clearly preferred. Differences with regard to cofactor preference and stability are also noted. The outer segment enzyme clearly functions in the rhodopsin cycle. It is unlikely that the 11-cis retinol dehydrogenase from pigment epithelium is directly involved in providing 11-cis retinaldehyde from rhodopsin regeneration, but it may serve to make available 11-cis retinaldehyde from rhodopdsin, digested in phagocytized rod sacs, for the synthesis of visual pigment by the visual cells.

Alcohol Oxidoreductases↗

PubMed1977

Effects of visual deprivation on polyribosome aggregation in visual cortex of the cat.

Neurons in the visual cortex of 48 normal and visually deprived kittens and cats were examined electron microscopically for the presence of absence of polyribosomes in their perikaryal cytoplasm. In normal animals at most ages the ribosomes of cortical neurons were aggregated into polysomes, but during the second and third months of life -- a period corresponding approximately to the physiologically defined critical period -- variable numbers of cells were found which contained ribosomes only in the monomeric form. The affected cells were spiny stellate neurons in the fourth layer of the cortex. Even within the critical period, however, cells with dispersed ribosomes were not found in every animal examined.

Animals↗

PubMed1988

Influence of visual deprivation on the visual and oculomotor system: acetylcholinesterase activity in oculomotor neurons.

The effects of visual deprivation (dark-rearing) on neurons in both the visual and oculomotor systems of black mice were studied using morphologic and histochemical techniques. In the neurons of the dorsal nucleus of the lateral geniculate body, the cytoplasm of dark-reared mice was less developed and the cytoplasm/nucleus ratio was significantly smaller in the dark-reared mice than in the controls. In contrast, large motoneurons in the oculomotor nucleus did not show any ultrastructural changes and the cytoplasm/nucleus ratio was normal. However, in large motoneurons of dark-reared mice, acetylcholinesterase (AChE)-positive areas were scattered in the cytoplasm, and the ratio of the AChE-positive areas to the cytoplasm area was significantly smaller than that in the controls.

Acetylcholinesterase↗

PubMed1994

Eye proprioception and visual localization in humans: influence of ocular dominance and visual context.

It has been previously established that the application of low amplitude mechanical vibrations to the inferior rectus muscle of human subjects results in an illusory upward movement of a luminous spot fixated in total darkness, and in a corresponding overshooting of the target when the subject is asked to point to this spot. In the first experiment described here, we compared the effects of applying vibrations to each eye separately and to both eyes simultaneously, under monocular and binocular viewing conditions, in left- and right-eyed subjects. The results confirmed that proprioceptive signals arising from both eyes are involved in egocentric visual localization. A proprioceptive dominance was observed however since vibration of the dominant eye gave rise to larger pointing displacements. In addition, whichever eye was stimulated, the pointing shift induced by vibrating a covered eye was of smaller amplitude than that which occurred when vibrations were applied to the viewing eye. The second experiment showed that both the vibration induced illusions and the pointing shifts disappeared in a structured visual context, which suggests that the processes involved when the target is viewed in darkness might differ from those occurring in structured surroundings.

Eye Movements↗

PubMed2002

Prehatching visual experience and lateralization in the visual Wulst of the chick.

We revealed functional lateralization of the chick visual system by placing injections of monosodium glutamate (0.5 microl, 100 mM) into the left or right Wulst regions of the hemispheres, and examined the effects of light experience before hatching on this lateralization. Following exposure of the left or right eye to light for 24 h beginning on day 18 of incubation, the chick's ability to categorize grain as distinct from pebbles was impaired by glutamate treatment of the Wulst contralateral to the exposed eye. Attack and copulation scores were also elevated. Following incubation of the eggs in darkness or with both eyes exposed to light, treatment of neither the left or right Wulst affected performance on the pebble-grain task: showing that either the left and right Wulst can assume control of this function. Treatment of either the left or right Wulst of these chicks elevates attack and copulation. However, examination of the distribution of attack scores revealed a bimodality in the attack scores of the chicks treated with glutamate in the right Wulst and not those treated in the left Wulst. In summary, light stimulation of one eye during a critical period of embryonic development causes the visual Wulst contralateral to the light exposed eye to develop dominance over its equivalent region in the other hemisphere. Without this lateralized stimulation of light both the left and right Wulst regions are largely but not exactly equivalent.

Aggression↗

PubMed1976

INDSCAL analysis of perceptual judgments for 24 consonants via visual, tactile, and visual-tactile inputs.

Twenty-four normal-hearing subjects received CV stimuli of uni- and bisensory inputs through the visual (speechreading), tactile (touch), and visual-tactile (speechreading and touch) modalities. Stimuli were presented via either a videotape monitor or a tactile vibrator or both. The purposes were to investigate the contribution of the tactile modality in uni- and bisensory conditions, and to analyze consonantal substitution errors to find perceptual features utilized by the subjects in their decision-making processes. The subjects' consonantal perceptions were phonetically transcribed and submitted to INDSCAL analysis which yielded mainly a four-dimensional solution. The interpretations of these dimensions were primarily closed bilabial, easy to see/hard to see, voiced/voiceless, and front/back place. Additional features were retrieved, but occurred less consistently.

Analysis of Variance↗

PubMed2006

Visual and both non-visual arrestins in their "inactive" conformation bind JNK3 and Mdm2 and relocalize them from the nucleus to the cytoplasm.

Arrestins bind active phosphorylated G protein-coupled receptors, terminating G protein activation. Receptor-bound non-visual arrestins interact with numerous partners, redirecting signaling to alternative pathways. Arrestins also have nuclear localization and nuclear exclusion signals and shuttle between the nucleus and the cytoplasm. Constitutively shuttling proteins often redistribute their interaction partners between the two compartments. Here we took advantage of the nucleoplasmic shuttling of free arrestins and used a "nuclear exclusion assay" to study their interactions with two proteins involved in "life-and-death" decisions in the cell, the kinase JNK3 and the ubiquitin ligase Mdm2. In human embryonic kidney 293 cells green fluorescent protein (GFP)-JNK3 and GFP-Mdm2 predominantly localize in the nucleus, whereas visual arrestin, arrestin2(Q394L) mutant equipped with the nuclear exclusion signal, and arrestin3 localize exclusively to the cytoplasm. Coexpression of arrestins moves both GFP-JNK3 and GFP-Mdm2 to the cytoplasm. Arrestin mutants "frozen" in the basal conformation are the most efficacious. Thus, arrestins in their basal state interact with JNK3 and Mdm2, suggesting that arrestins are likely "preloaded" with their interaction partners when they bind the receptor. Robust interaction of free arrestins with JNK3 and Mdm2 and their ability to regulate subcellular localization of these proteins may play an important role in the survival of photoreceptors and other neurons, as well as in retinal and neuronal degeneration.

Animals↗

PubMedDate not supplied

Studies on hand-held visual communication device for the deaf and speech-impaired I. Visual display window size.

Messages were presented which moved from right to left along an electronic alphabetic display which was varied in "window" size from 4 through 32 letter spaces. Deaf subjects signed the messages they perceived. Relatively few errors were made even at the highest rate of presentation, which corresponded to a typing rate of 60 words/min. It is concluded that many deaf persons can make effective use of a small visual display. A reduced cost is then possible for visual communication instruments for these people through reduced display size. Deaf subjects who can profit from a small display can be located by a sentence test administered by tape recorder which drives the display of the communication device by means of the standard code of the deaf teletype network.

Adult↗