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Results for “visualization”

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PubMed1976

[Effect of visual deprivation on the composition of structural proteins of the visual system of rabbit brain].

Composition of membrane proteins of the visual system structures of normal and dark-reared rabbits (for 2 1/2 months from birth) was studied by using polyacrylamide gel electrophoresis. Solubilization of membrane proteins was carried out using a 1% solution of Triton X-100 and a 0.1% solution of sodium dodecylsulfate, in succession. One fraction representing the fraction of high-molecular proteins was absent in membrane proteins of the visual analyser in the dark-reared animals; there was also a change in the percentage content of proteins in different fractions in comparison with the normal. The data obtained led to the conclusion that visual deprivation caused marked quantitative and qualitative reconstruction in the composition of membrane proteins of the brain with some specific characteristics for the formation of the visual analyser.

Animals↗

PubMed1999

Visual segmentation by contextual influences via intra-cortical interactions in the primary visual cortex.

Stimuli outside classical receptive fields have been shown to exert a significant influence over the activities of neurons in the primary visual cortex. We propose that contextual influences are used for pre-attentive visual segmentation. The difference between contextual influences near and far from region boundaries makes neural activities near region boundaries higher than elsewhere, making boundaries more salient for perceptual pop-out. The cortex thus computes global region boundaries by detecting the breakdown of homogeneity or translation invariance in the input, using local intra-cortical interactions mediated by the horizontal connections. This proposal is implemented in a biologically based model of V1, and demonstrated using examples of texture segmentation and figure-ground segregation. The model is also the first that performs texture or region segmentation in exactly the same neural circuit that solves the dual problem of the enhancement of contours, as is suggested by experimental observations. The computational framework in this model is simpler than previous approaches, making it implementable by V1 mechanisms, though higher-level visual mechanisms are needed to refine its output. However, it easily handles a class of segmentation problems that are known to be tricky. Its behaviour is compared with psycho-physical and physiological data on segmentation, contour enhancement, contextual influences and other phenomena such as asymmetry in visual search.

Models, Neurological↗

PubMed1999

From visual experience to visual function: roles of neurotrophins.

Recently, a role for neurotrophins in regulating cortical developmental plasticity has clearly emerged. We present in this review a summary of the early data on the action of nerve growth factor (NGF) in visual cortical development and plasticity in the rat and of other neurotrophins in the visual cortex of other mammals. In addition, to clarify the differences in the results obtained with the various neurotrophins in different animal preparations, we also report new data on the action of NGF, brain-derived neurotrophic factor (BDNF), neurotrophin (NT)3, and NT4 in the same preparation-namely, the visual cortex of the rat. We discuss old and new results in a physiological model in which different neurotrophins play different roles in regulating visual cortical development and plasticity by acting on different neural targets, such as lateral geniculate nucleus (LGN) afferents, intracortical circuitry, and subcortical afferents, and propose a tentative scheme summarizing these actions.

Animals↗

PubMed2000

Effects of superior colliculus inhibition on visual motion processing in the lateral suprasylvian visual area of the cat.

PURPOSE: To clarify whether visual inputs of the tectothalamocortical pathway influence motion processing within the lateral suprasylvian (LS) area of the cat. METHODS: This study was conducted in five cats. Tungsten microelectrodes were used for recording visual evoked potentials. The electrodes were introduced into the LS area. An array of 120 randomly located dots was projected onto the stimulus field (40 degrees x 40 degrees) in front of the animal by a slide projector. The dots were moved rightward and leftward alternatively with interstimulus intervals by a mirror attached to a galvanometer, the movements of which were controlled by a microcomputer. Each motion sequence consisted of an abrupt onset of motion that continued for 100 msec followed by an abrupt offset and a stationary phase of 900 msec; the total duration of each sequence was thus 1000 msec. The velocity of the motion was varied in 12 steps. The onset of motion was used as the trigger for recording evoked potentials. Single or multiple injections (two to three) of muscimol were made, mainly into the rostral superior colliculus (SC). The amplitudes of evoked potentials before and after the muscimol injection were compared. RESULTS: A large negative wave (N1) with the peak latency of 89.80+/-16.39 msec (mean +/- SD, n = 191) was recorded consistently. The amplitude of N1 was not altered by the muscimol injection into the SC when the velocity of motion was 50 deg/sec or less. When the velocity of motion was 75 deg/sec or more, however, the amplitude of N1 was reduced to 62% to 72% of that noted before the muscimol injection. CONCLUSIONS: These findings suggest that the LS area processes the visual motion inputs reaching through the two parallel pathways, the geniculostriate pathway and the tectothalamocortical pathway, when the velocity of visual motion is 75 deg/sec or more.

Animals↗

PubMed2003

Changes of visual function and visual ability in daily life following cataract surgery.

PURPOSE: To examine best corrected visual acuity (BCVA), contrast sensitivity (CS) and functional visual complaints in early cataract and after the cataract surgery. PATIENTS AND METHODS: 53 eyes with early cataract (BCVA 20/30: Snellen charts) were examined before the surgery as well as 12 months after the surgery. BCVA was tested using logMAR chart. CS was examined using VCTS chart in 6 spatial frequencies. Influence of glare was tested using BAT. Patients' subjective visual functions were evaluted using a questionnaire (distance vision, near vision, mesopic vision and glare conditions). 22 subjects were examined as control group. RESULTS: BCVA was 0.52 (0.22-1.05) preoperatively and 0.83 (0.37-1.26) postoperatively. BCVA in patients in both terms was significantly lower compared to the control group. CS in patients before surgery was significantly lower compared to controls, postoperatively improved significantly and was only nonsignificantly lower compared to controls except for the highest spatial frequency. Glare had only nonsignificant influence. The questionnaire scores were correlated with visual performance in both terms. CONCLUSIONS: The significant improvement of both BCVA and CS suggest that cataract surgery improves quality of life in early cataract. Questionnaire should be considered as adjuncts to BCVA and CS in evaluating early cataract.

Adult↗

PubMed1992

Visual projections routed to the auditory pathway in ferrets: receptive fields of visual neurons in primary auditory cortex.

How does cortex that normally processes inputs from one sensory modality respond when provided with input from a different modality? We have addressed such a question with an experimental preparation in which retinal input is routed to the auditory pathway in ferrets. Following neonatal surgical manipulations, a specific population of retinal ganglion cells is induced to innervate the auditory thalamus and provides visual input to cells in auditory cortex (Sur et al., 1988). We have now examined in detail the visual response properties of single cells in primary auditory cortex (A1) of these rewired animals and compared the responses to those in primary visual cortex (V1) of normal animals. Cells in A1 of rewired animals differed from cells in normal V1: they exhibited larger receptive field sizes and poorer visual responsivity, and responded with longer latencies to electrical stimulation of their inputs. However, striking similarities were also found. Like cells in normal V1, A1 cells in rewired animals exhibited orientation and direction selectivity and had simple and complex receptive field organizations. Furthermore, the degree of orientation and directional selectivity as well as the proportions of simple, complex, and nonoriented cells found in A1 and V1 were very similar. These results have significant implications for possible commonalities in intracortical processing circuits between sensory cortices, and for the role of inputs in specifying intracortical circuitry.

Animals↗

PubMed1990

Visually evoked potentials and simple reaction times to visual stimuli in chronic disulphide intoxication.

The relationship between parameters of visually evoked potentials (VEPs) and the results of a psychological test assessing the speed of motor reaction to visual stimuli was examined in 21 patients with chronic carbon disulphide intoxication. Correlations obtained suggest cerebral disfunction of the visual pathway and diminished ability to transform visual information to motor reaction at the level of the cortical association centre.

Adult↗

PubMedDate not supplied

[The effect of early visual deprivation on the synthesis of glutamic and aspartic acids in mitochondria of central structures of the visual analyzer in the dog].

After 45 days visual deprivation synthesis via direct reductive amination and transamination of glutamic and aspartic acids was inhibited in mitochondria of dog visual cortex, colliculi anterioris and corpus geniculatum externus. Under conditions of long-term (90 days) visual deprivation synthesis of glutamic and aspartic acids was less effectively inhibited in mitochondria of the brain areas studied via the reductive amination and transamination, except of the aspartic acid synthesis by means of transamination, the rate of which was maintained at the level similar to the values observed after 45 days of visual deprivation.

Amination↗

PubMed1988

Sustained visual attention in young infants measured with an adapted version of the visual preference paradigm.

Phases of infant visual attention were studied using a visual preference procedure that was modified to be similar to a "dual-task," interrupted stimulus procedure. Infants were tested in a cross-sectional design at 14, 20, or 26 weeks of age. The infants were presented with varying and complex TV patterns on a TV monitor. At a delay from the onset of fixation on this stimulus, a similar pattern was presented on an adjacent TV monitor within the infant's field of vision. This secondary stimulus was presented either when heart rate (HR) decelerated significantly below prestimulus level or when the HR returned to prestimulus level. These 2 conditions correspond to sustained attention and attention termination phases of visual attention. The infants were less easily distracted by the secondary stimulus when HR was lower than prestimulus level than when it had returned to prestimulus levels. The amount of HR slowing on the HR deceleration trials increased over this age range, suggesting a developmental increase in sustained attention across this age range. The HR response at the time the infant looked at the secondary stimulus was different for the 2 delay conditions and differed from the HR response at primary stimulus onset. These results confirm the existence of distinct phases of attention during the visual preference procedure and suggest a refinement of the use of simple fixation time as a measure of infant attention with this procedure.

Arousal↗

PubMedDate not supplied

[Visual evoked potentials and the time of motor reaction to visual stimuli in chronic metallic mercury poisoning].

In a group of 10 patients with diagnosed occupational chronic poisoning with metallic mercury a correlation was sought between the parameters of the visual evoked potentials and the results of the psychological test evaluating the rapidity of motor response to the visual stimuli. The analysis suggest a cerebral dysfunction of the visual neurons and reduced rate of visual information transformation to the motor effector at the level of the cortical association centre.

Adult↗

PubMed1985

Deficits in visual motion processing following ibotenic acid lesions of the middle temporal visual area of the macaque monkey.

Physiological experiments have produced evidence that the middle temporal visual area (MT) of the monkey is selectively involved in the analysis of visual motion. We tested this hypothesis by studying the effects of small chemical lesions of MT on eye movements made in response to moving as opposed to stationary visual targets. We observed two deficits for eye movements made to moving targets: a monkey's ability to match the speed of his smooth pursuit eye movements to the speed of the moving target was impaired, and a monkey's ability to adjust the amplitude of a saccadic eye movement to compensate for target motion was impaired. In contrast, saccades to stationary targets were unaffected by the MT lesions, suggesting that monkeys with MT lesions had more difficulty responding to moving than to stationary stimuli. These results provide the first behavioral evidence that neural processing in MT contributes to the cortical analysis of visual motion.

Animals↗

PubMed1993

[The central visual field defects in low-tension glaucoma. A comparison of the central visual field defects in low-tension glaucoma with those in primary open angle glaucoma].

To discover if there is difference in central visual field damage between low-tension glaucoma (LTG) and primary open angle glaucoma (POAG) eyes, the data obtained with the 10-2 threshold program of the Humphrey visual field analyzer were analysed using logistic discriminant analysis. One hundred and four LTG eyes from 65 case (maximum IOP < or = 21 mmHg) and 48 POAG eyes from 34 cases (maximum IOP > or = 25 mmHg) with early to moderately advanced visual field damage were included. There was no significant difference in mean deviation (MD, STATPAC), refraction, or age between the 2 groups. The analysis demonstrated that an arcuate area in the upper central 5-10 degrees of the visual field was significantly more depressed in LTG than in POAG eyes.

Aged↗

PubMed1996

Interruption of visual deprivation during development restores the normal density of peptidergic neurons in the rat visual cortex.

We have previously shown that dark rearing moderates the normal decline in the number of somatostatin (SRIF) and neuropeptide (NPY) neurons in the developing rat visual cortex. Thus, cortical areas of visually deprived animals at postnatal day (P) 60 contain consistently more SRIF and NPY neurons than do the same areas of rats reared in normal lighting conditions. In present study animals were reared in darkness from birth to P14, P21, P30 or P60 and then placed in ambient light conditions up to the day of sacrifice (P60 or P90). Counting of immunocytochemically identified SRIF and NPY neurons in all cortical visual areas of these and of undeprived animals, showed that interruption of visual deprivation during both the early or the late stages of postnatal development restores the normal density of the above peptidergic neurons.

Animals↗

PubMed1997

[Influence of visual stimuli on eye-position related activities of neurons in primary visual cortex (V1) of awake monkeys].

Extracellular recordings were made in the primary visual cortex (V1) in two awake monkeys to test the influence of visual stimuli on the eye-position related activites of the neurons. While the monkeys gazed on a fixation point (FP) positioned sequentially at different locations on a TV screen, two types of visual stimuli were presented on the same screen: (1) A small light ring flashed repeatedly around the FP or (2) A prefered light bar shifted continuously across the cell's receptive field (RF). Both stimuli significantly enhanced the eye-position related activities and correspondingly increased the incidence of the eye-position dependent neurons. The results show that the integration of information on vision and on eye position may take place at quite the earliest stage of the visual cortices.

Animals↗

PubMed1976

Physiological aspects of visual perception. I. Functional aspects of visual cortex.

The first part of the Bennett Lecture for 1975 is a description of the dissociation of visual perception in the macaque monkey by ablation of area 17 on the one hand, and of areas 18 and 19 on the other. Bilateral removal of area 17, with careful preservation of a great part of areas 18 and 19, and of the inferior pulvinar, resulted in loss of binocular fixation, loss of visual recognition of still objects, and loss of visuosocial behavior such as grimacing and vocalization. There remained excellent visuospatial orientation and reaching for moving peripheral visual targets. Removal of areas 18 and 19, with isolation of area 17 from the remainder of cortex, was accomplished in two animals and left intact the ability to distinguish and sort out still objects by vision, with intact fixation, and visuosocial behavior. Spatial orientation was then easily confused by movement.

Animals↗

PubMed1986

Ventral posterior visual area of the macaque: visual topography and areal boundaries.

Using both physiological and anatomical techniques, we have studied the topographic organization of extrastriate visual cortex on the ventral surface of the occipital lobe in macaque monkeys. Our results show that a topographically organized representation of the superior contralateral quadrant of the visual field lies immediately anterior to the ventral half of V2. This area is organized in a mirror symmetric fashion to ventral V2: it shares a horizontal meridian representation with V2 and a representation of the superior vertical meridian forms its anterior border. A well-defined strip of callosal inputs runs along the vertical meridian representation, thereby providing a reliable anatomical marker for areal boundaries in ventral extrastriate cortex. We refer to this area as the ventral posterior area (VP) because it is, in all these respects, notably similar to VP in the owl monkey. Ventral V2 has strong reciprocal connections with VP, and the topography of the V2 projection agrees closely with the topography revealed in our physiological mapping experiments. The visual field representation in VP is strikingly anisotropic, with linear magnification factor being much larger along contours of constant polar angle than along contours of constant eccentricity.

Animals↗

PubMed1975

Development of visually evoked responses and visually guided behavior in kittens: effects of superior colliculus and lateral geniculate lesions.

The development of visually evoked responses (VER's) and visually guided behavior was studied in kittens for 3 months after unilateral lesions of the superior colliculus (SC) or lateral geniculate nucleus (LGN) made at an early age. Of 37 kittens studied, data are presented for 6 which met 3 criteria: survival to at least 90 days of age; adequate lesion size and location; and technically satisfactory VER's and behavioral observations at appropriate intervals. The SC and LGN lesions markedly reduced or eliminated different VER components in infancy, but only the effects of LGN lesions persisted to 3 months of age. Visual field behavior deficits occurred following both types of lesions, but only those following SC lesions persisted to 3 months of age. These results are interpreted in terms of the functional status of the structures mediating the VER's and behavior at the time the lesions were made.

Animals↗

PubMed1989

Visual field in hysteria-reliability of visual field by Goldmann perimetry.

Four cases with hysterical amblyopia in youngsters under 15-year-old showed the poor reproducibility of visual field, that is, when the same target was moved from the periphery toward the fixation ten times along the same meridian during the same examination, the position of the plotted points were rather variable. The range of variation was measured from the innermost point to the outermost one, after the two first points were omitted because points first detected were usually far from the others. The variation of cases measured by this method was compared with that of normal persons. Results were as follows; 1. in normal person, the mean value of its range was 5.5 degrees in first decade and 4.2 degrees in second to seventh decade; 2. patients with psychogenic visual disturbances showed a variability of 14.2 degrees, and this was significantly different from normal (p less than 0.01). These results suggest that this convenient method was helpful for diagnosis of hysteria. It should also be remembered that when we evaluate the visual field, changes under 4 degrees are probably not significant.

Adolescent↗