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PubMed1998

Visual input evokes transient and strong shunting inhibition in visual cortical neurons.

The function and nature of inhibition of neurons in the visual cortex have been the focus of both experimental and theoretical investigations. There are two ways in which inhibition can suppress synaptic excitation. In hyperpolarizing inhibition, negative and positive currents sum linearly to produce a net change in membrane potential. In contrast, shunting inhibition acts nonlinearly by causing an increase in membrane conductance; this divides the amplitude of the excitatory response. Visually evoked changes in membrane conductance have been reported to be nonsignificant or weak, supporting the hyperpolarization mode of inhibition. Here we present a new approach to studying inhibition that is based on in vivo whole-cell voltage clamping. This technique allows the continuous measurement of conductance dynamics during visual activation. We show, in neurons of cat primary visual cortex, that the response to optimally orientated flashed bars can increase the somatic input conductance to more than three times that of the resting state. The short latency of the visually evoked peak of conductance, and its apparent reversal potential suggest a dominant contribution from gamma-aminobutyric acid ((GABA)A) receptor-mediated synapses. We propose that nonlinear shunting inhibition may act during the initial stage of visual cortical processing, setting the balance between opponent 'On' and 'Off' responses in different locations of the visual receptive field.

Animals↗

PubMed1992

Visual acuity and visual field development after cryocoagulation in infants with retinopathy of prematurity.

Visual development was studied in 10 very-low-birth-weight infants (less than 1500 g) with retinopathy of prematurity (ROP) stage 3+ who had been treated with cryocoagulation in both eyes. Binocular visual acuity (acuity cards method) and binocular visual fields (kinetic perimetry) were assessed repeatedly in the first year of life. At 12 months corrected age, visual acuity was normal in seven and impaired in three infants, who appeared to be severely myopic. Normal visual fields were found in eight infants at this age. The results indicate that cryotherapy in cases of ROP stage 3+ does not interfere with visual acuity development. The effect on visual field development needs further investigation.

Cryosurgery↗

PubMed1997

Constructional dyspraxia in preterm diplegia: isolation from visual and visual perceptual impairments.

OBJECTIVE: To evaluate ophthalmological profiles, visual perception and constructional function in preterm children with spastic diplegia (SD) and to clarify their neuropsychological deficits in comparison with a control group. METHODS: Thirty-five SD and 34 control children were investigated for visual acuity, eye position, stereoacuity, depth perception, visual perception, visuo-spatial construction and constructional praxis. Each of the results was compared among the four groups as SD with and without strabismus, and control with and without strabismus. RESULTS: Strabismic SD showed worse visual acuity, worse stereoacuity and worse depth perception than the other groups. Constructional dyspraxia was detected in 94.1% of SD either with or without strabismus, while it was rare in the control group. There was no significant contribution of visual acuity, eye position, stereoacuity or depth perception to constructional dyspraxia by stepwise multiple linear regression analysis. CONCLUSION: Strabismic preterm SD children are at high risk for visual dysfunction. Constructional dyspraxia was frequently found in SD children and may be a dysfunction isolated from ophthalmological and visual perceptual dysfunctions.

Adolescent↗

PubMed1998

Visual behaviours of neurologically impaired children with cerebral visual impairment: an ethological study.

BACKGROUND/AIMS: Visual functions of neurologically impaired children with permanent cerebral visual impairment (CVI) can be difficult to determine. This study investigated the behavioural profile of CVI children by means of ethological observations in order to gain a better understanding of their visual functions. METHODS: Video registrations of nine subjects who were unable to undergo more orthodox methods of visual function testing were observed and analysed by an ethologist. RESULTS: A series of behaviours (direct signs) and supportive or confirming behavioural elements (indirect signs) indicating some visual perception in the children were found. CONCLUSION: Detailed ethological observations of visual behaviour were shown to be useful for analysing visual functions of children with permanent CVI.

Blinking↗

PubMedDate not supplied

Visual hand display (VHD) as an introductory procedure for measuring vision in infants and young children with visual impairment.

We developed the Visual Hand Display (VHD) to measure vision in visually impaired infants and young children. The VHD is a circular fabric mitten, which is held easily by inserting the hand between the two surfaces. Black-and-white stripes are attached to one surface, 25, 15, 10, 4, and 2 mm per stripe. The VHD acuity is determined by the shortest test distance and the smallest stripes that the patient can detect. The VHD acuities were compared with preferential looking (PL) staircase acuities in 130 patients (53 males, 77 females; age range, 2 to 13 years; median, 21.0 months). Of these, 107 (82.3%) had various degrees of retinopathy of prematurity. The correlation between the VHD and the PL acuities was high (R2 = 0.849). PL acuities were better than the VHD acuities in 98/130 patients (75.4%), with an average difference of 0.51 (SD = 0.70) octave. The visual acuity differences were more pronounced in subjects with slight visual impairment and much less in subjects with severe visual impairment. The VHD seems to be an effective introductory method to evaluate visual acuity in severely visually impaired infants and young children. This method also would be effective with severely mentally and physically disabled patients who cannot undergo PL testing.

Adolescent↗

PubMed1992

The effect of visual experience on development of NMDA receptor synaptic transmission in kitten visual cortex.

We have studied the effect of dark rearing on the development of excitatory amino acid transmission in 6-week-old kittens. In normal kittens, the NMDA component of the visual response decreases between 3 and 6 weeks of age for cells located in layers IV, V, and VI (Fox et al., 1991). Dark rearing to 6 weeks of age prevents this decrease. Subsequent exposure to light allows the decrease to proceed. Ten days in the light after 6 weeks in the dark was sufficient to decrease the NMDA component of the visual response to the same levels seen in light-reared animals of the same age. Comparison of the effect of the non-NMDA antagonist 6-cyano-7-dinitroquinoxaline-2,3-dione with the NMDA antagonist aminophosphonovalerate showed that the changes were due to the relative contributions of NMDA and non-NMDA receptors to the visual response rather than the overall contribution of glutamate receptors. We also studied the receptive field properties of the cells in the various groups of kittens. Cells given 4 d in the light after 6 weeks in the dark showed increased direction selectivity but little change in response firing rate. After 10 d in the light, visual responses did show some recovery toward adult values, but neither average firing rates nor the proportion of direction-selective cells reached the levels found in normal 6-week-old animals, contrary to the suggestion that a short period in the light can reverse the effect of dark rearing completely. These results show that the decrease in the NMDA component of the visual response seen during normal development of the cortex is caused by visual experience. Changes in NMDA receptors and developmental events such as geniculocortical afferent segregation and acquisition of orientation tuning covary as a function of visual experience rather than age, strongly suggesting that NMDA receptors are involved in experience-dependent developmental processes.

2-Amino-5-phosphonovalerate↗

PubMed1991

Flash visual-evoked potentials and flash electroretinography in the preoperative visual prognosis of eyes with cataracts.

This study evaluated the reliability of flash visual-evoked potentials and flash electroretinography in the prognosis of postoperative visual acuity after cataract extraction. We tested 94 patients with cataract in whom the preoperative visual acuity ranged from light perception to 3/10. On the basis of the electrophysiologic tests, we formulated three types of preoperative visual prognosis: high, intermediate, and poor. To assess the postoperative visual acuity, all subjects were followed for at least three months after cataract extraction. Visual acuity was subdivided in three arbitrary classes: less than or equal to 1/10, between 2/10 and 5/10, and between 6/10 and 10/10. Finally, we evaluated the reliability of our preoperative prognosis. Statistical analysis of our results (using the chi-square test) showed our predictions were highly significant for the total sample, revealing a strict correlation between our prognosis and the final visual acuity.

Adult↗

PubMed1990

The predictability of infant visual-evoked response testing on future visual acuity.

We reviewed the records of 27 infants with abnormal eye examinations and visual-evoked response (VER) testing (mean age, 10.5 months) who subsequently underwent a long-term follow-up ophthalmology examination (mean duration, 41 months). The infants were initially diagnosed with various ocular disorders including cortical blindness (eight), optic nerve hypoplasia (six), congenital cataract (two), and retinopathy of prematurity (one). Standard optotype visual-acuity determinations were available in the follow-up records of 11 children (21 eyes), and fixation behavior was obtained in the remaining 16 children (32 eyes). Results revealed that pattern-reversal VER P1 latency was predictive (87%) of whether visual acuity was equal to (or better than) or worse than 20/100 and whether a patient would have good fixation behavior (fix and follow, FF) or poor fixation (no FF) (86%) (P less than .001). Although flash VER P1 latency was also predictive of later visual acuity or good fixation (73%), it was not statistically significant. Pattern VER P1 amplitude and flash VER P1 amplitude were not predictive of later visual function. The predictive power of pattern VER P1 latency for later visual function probably relates to its reflection of macular function and low variability. An analysis of the variability of each of the four VER factors in normal infants (n = 50) indicated that pattern VER P1 latency was the least variable, and consequently most sensitive, VER factor for detecting and quantifying pathology. Overall, the results of this retrospective study suggest that pattern VER P1 latency may have important predictive power for later visual function in infants with an initially abnormal ophthalmologic examination.

Evoked Potentials, Visual↗

PubMed1989

[Visual perception in normal children and adults I. Developmental changes in dominance of visual field in normal children].

Developmental changes of dominance of visual field was evaluated using a tachistoscope in 70 normal subjects from 4 years of age up to adulthood (35 males and 35 females). The time of exposure was measured under two experimental conditions; simultaneous stimulation of different types to both left and right fields, or a single stimulus only to one visual field. One of the following stimuli was exposed to the visual field; one, two or three letters of Japanese characters ("hirakana"), one of Chinese characters ("kanji"), figures, and Roman alphabets. Simultaneous bilateral stimulation revealed frequent dominance in the right visual field, which was established by 4 years of age. The average time of exposure become shorter with age up to 6-7 years for one "hirakana" letter and one "kanji", and up to 10 years for two and three "hirakana" letters. All four left-handed subjects in this study showed dominance of the right visual field. Dominance of the left visual field was observed in 3 of 52 subjects with dominance of the right eye (5.8%), and in 5 of 15 with dominance of the left eye (33.3%). This difference was statistically significant (chi 2 = 8.41, p less than 0.01). It was suggested that dominance of the visual field was related with dominance of the eye, and not with handedness.

Adolescent↗

PubMed1989

[Visual perception in normal children and adults II. Correlation between dominance of visual field and dominance of the eye].

To clarify more precisely about the correlation between the dominance of visual field and dominance of the eye, tachistoscopic examination was performed on 48 normal adults; 24 males and 24 females, and 24 right-handed and 24 left-handed subjects. The mean of the time of exposure was less than 4.5 msec. The time of exposure was independent of handedness, dominance of the eye, sex, or the type of stimulus. Four right-handed and four left-handed subjects showed dominance of the left visual field for the A value, suggesting no correlation between handedness and dominance of the visual field. However, six of those eight subjects were found to have dominance of the left eye for the A value, and all seven subjects with dominance of the left visual field for the D value showed dominance of the left eye (chi 2 = 16.39, p less than 0.001). It was concluded that dominance of the eye was significantly correlated with visual field. It is therefore important to examine dominance of the eye as well as dominance of the visual field for evaluation of cerebral dominance with regard to visual perception.

Adult↗

PubMedDate not supplied

[Age dynamics of visually guided behavior and visual evoked potentials of altricial nestlings].

Comparative study has been carried out of factors of organization of visually guided feeding behaviour (observation method) and the degree of maturity of the visual mechanisms by the criterion of Wulst EPs formation and of their recovery cycles in normally developing and visually deprived nestlings. In has been established that during the period following the opening of the eyes (5-9th day) the feeding behaviour is connected with diffuse photo-sensitivity of visual mechanisms. Diffuse photo-sensitivity fully provides for natural feeding behaviour at the corresponding stage of development of visual functions. Complete visual deprivation during the whole period of diffuse photo-sensitivity does not influence subsequent development of the visual system.

Age Factors↗

PubMed1987

Functional properties of parietal visual neurons: radial organization of directionalities within the visual field.

Parietal visual neurons (PVNs) were studied in waking monkeys as they executed a simple fixation-detection task. Test visual stimuli of varied direction, speed, and extent were presented during the fixation period; these stimuli did not control behavior. Most PVNs subtend large, bilateral receptive fields and are exquisitely sensitive to stimulus motion and direction but insensitive to stimulus speed. The directional preferences of PVNs along meridians are opponently organized, with the preferred directions pointing either inward toward or outward away from the fixation point. Evidence presented in the preceding paper (Motter et al., 1987) indicates that opponent directionality along a single meridian is produced by a feed-forward inhibition of 20 degrees-30 degrees spatial extent. The observations fit a double-Gaussian model of superimposed but unequal excitatory and inhibitory receptive fields: When the former is larger, inward directionality results; when smaller, outward directionality results. We examine here the distribution of the meridional directional preferences in the visual field. Tests showed that opponent organization is not produced by differences in local directional properties in different parts of the receptive field. The distribution of response intensities from one meridian to another is adequately described by a sine wave function. These data indicate a best radial direction for each neuron with a broad distribution of response intensities over successive meridians. Thus, any single PVN, with rare exceptions, cannot signal radial stimulus direction precisely. We then determined how accurately the population response predicted radial stimulus direction by the application of a linear vector summation model. The resulting population vector varied from stimulus direction by an average of 9 degrees. Whether or not the perception of the direction of motion depends upon a population vector remains uncertain. PVNs are especially sensitive to object movement in the visual surround, particularly in the periphery of the visual field. This, combined with their large receptive fields and their wide but flat sensitivity to stimulus speed, makes them especially sensitive to optic flow. This is discussed in relation to the role of the parietal visual system in the visual guidance of projected movements of the arm and hand, in the guidance of locomotion, and in evoking the illusion of vection.

Action Potentials↗

PubMed1979

Visual-vestibular interactions: I. Influence of peripheral vision on suppression of the vestibulo-ocular reflex and visual acuity.

Legibility of head-fixed displays in some motion environments is partially dependent upon visual suppression of the vestibuloocular reflex (VOR). This study investigates the effects of differing relationships between peripheral background movement and whole-body motion on the VOR and on visual performance. The purpose of the study is to explore factors in motion environments that influence performance limits and to develop procedures of potential usefulness in evaluating interacting visual and vestibular function. Visual performance and visual suppression of the VOR were markedly different, depending upon the relative direction of peripheral background movement. Visual suppression of the VOR, and visual performance, were disrupted far more when vestibular inputs and peripheral optokinetic inputs were discordant than when they were concordant. Results have potential implications for head-up displays and suggest a procedure for evaluating visual/vestibular function.

Acceleration↗

PubMed1992

Steady-state visual evoked cortical potentials from stimulation of visual field quadrants. Optimizing pattern variables for the size of the field to be investigated.

The effects of check size and stimulus size were investigated to optimize the steady-state visual evoked cortical potentials from pattern-reversal stimulation of the visual field quadrants. Check sizes of 15', 30', 60', 90', 120' and 180' were investigated at a pattern reversal rate of 11.6 per second for field sizes varying from 2 degrees x 2 degrees to 24 degrees x 24 degrees. The visual evoked cortical potentials were recorded from mid occipital, right occipital and left occipital positions. In the inferonasal quadrant, the largest amplitudes were obtained with 30' and 60' check sizes; however, for these check sizes, the visual evoked cortical potential yielded limited additional information for field sizes greater than 4 degrees x 4 degrees and 6 degrees x 6 degrees, respectively. When a field size of 12 degrees x 12 degrees was investigated, a 90' check size was optimal. The results indicated that, with the above recording positions and check sizes of 15' to 120', there is an optimal number of pattern elements, 40 to 100, for stimulation of the inferonasal quadrant. This should be taken into account when a check size is selected to investigate a field quadrant of a particular size. Digital signal processing techniques were applied to analyze the visual evoked cortical potential, and the system shows promise for objective examination of the visual field.

Adult↗

PubMedDate not supplied

Automatic perimetry and visual P300: differences between upper and lower visual fields stimulation in healthy subjects.

Human visual-evoked potentials (VEPs) from upper and lower hemifield stimulation are thought to reflect the anatomical and functional differences between the hemiretinas and corresponding visual pathways. Conflicting results have, however, been reported in topographic studies on the putative cortical generators. We have estimated by automatic perimetry (Octopus 2000R, Program 32) and compared the sensitivity thresholds of lower and upper hemifields of the retina in 12 healthy subjects with no history or evidence of visual or neurological diseases. A visual P3 that is linked to cognitive function was recorded in an odd-ball paradigm with presentation of high-contrast checkerboards at two different spatial frequencies at 20 degrees eccentricity in each hemifield. VEP and P3 were recorded at O1 and O2 and at Cz according to the 10/20 international system. Lower sensitivity thresholds were found, and higher VEP and event-related potential (ERP) amplitude values were obtained when stimulating the lower, compared with the upper, visual hemifield. The results are consistent with previous findings and anatomical and physiological evidence in animals and man. Interactions between perceptive process in the visual system and higher cognitive functions are a possible explanation for this finding.

Adult↗

PubMed1990

Senescence of visual function as studied by visually evoked cortical potentials.

Visual functions in senescence were assessed quantitatively by the pattern reversal visually evoked cortical potentials (VECP) in human subjects and animals. The results obtained in the elderly showed an elevation of contrast threshold, ie, lowered sensitivity, for higher spatial frequency, and a rise in the luminance thresholds. There was also an overall suppression in the temporal frequency curves, a sensitivity decrease for the upper half of the visual field, a blue-yellow defect and a decrease in the amplitude of accommodation. Studies of the pseudophakic eye with an intraocular lens verified that the lower transparency and yellowish changes of the crystalline lens and senile miosis do not entirely account for the depressed visual function in the elderly. The delay of P100 peak latency of the VECP in patients with juvenile Parkinson's disease after cessation of L-dopa indicated the deficiency of dopamine in these patients, which in turn was considered as a clinical model of senescence. Optic nerve fiber counts in mice showed a significant decrease in the aged group. It was considered that there is neuronal senescence other than in the eye itself. The results can be illustrated by the following daily life experience. In the evening, an elderly person would have difficulty in identifying a cat as a calico cat if the cat were atop a wall and running quickly through the visual field. It was surprising, however, that the senescence found in the visual function was not as great as that found in the other sensory organs. As further studies, investigation of the feedback mechanism from the brain to the retina and the compensatory mechanism should be made.

Accommodation, Ocular↗

PubMed1988

Assessment of visual function in patients with age-related macular degeneration and low visual acuity.

The visual function of 100 eyes with low visual acuity of 100 patients with age-related macular degeneration was examined using measurements of visual acuity, peak contrast sensitivity, and the ability to read, to tell time, and to distinguish colors, products, and facial expressions. Visual acuity and peak contrast sensitivity were correlated (r = .62); however, a range of peak contrast sensitivities was observed at each level of acuity. When considered individually, visual acuity and peak contrast sensitivity were related to the ability to perform each of the tasks. When multivariate methods were applied, both visual acuity and peak contrast sensitivity contributed independently to the ability to read and tell time. Among patients with the same contrast sensitivity, visual acuity had little or no relationship to the ability to identify colors, products, and faces.

Aged↗

PubMed1981

Expansion of the ipsilateral visual corticotectal projection in hamsters subjected to partial lesions of the visual cortex during infancy: anatomical experiments.

Electrophysiological methods were employed to determine whether or not partial visual cortical lesions in neonatal (7--11-day) hamster produced large scotomas in the cortical visual representation. In cases where such scotomas were present electrophoretic deposits of radioactive amino acids in the visually responsive "cortical remnant" of the damaged hemisphere resulted in labelling throughout the lower portion of the stratum griseum superficiale and the stratum opticum of the ipsilateral superior colliculus. No differential labeling of the part of the colliculus which was topographically matched with the remaining visual representation in the cortical remnant was observed. In normal hamsters relatively localized, visual cortical deposits of radioactive amino acids resulted in superficial layer labeling only in portions of the colliculus which corresponded to the locus of the cortical deposit. In a similar fashion, small lesions at physiologically defined loci in the cortical remnant produced degeneration throughout most of the superficial tectal laminae, but a more restricted "focus" of denser degeneration was also visible in these cases. The position of this focus in the colliculus for a given cortical lesion varied with the nature of the visual map in the cortical remnant. In several additional neonatally brain-damaged hamsters large lesions of the visual cortex in the intact hemisphere were combined with radioactive amino acid deposits in the cortical remnant to determine whether or not axons from the crossed corticocollicular pathway previously demonstrated in such hamsters were intermingled with fibers from the ipsilateral corticotectal projection. In alternate sections processed for autoradiography or by the Fink-Heimer ('67) method autoradiographic label and degeneration argyrophilia were both observed in the medical part of the colliculus ipsilateral to the neonatal cortical lesion.

Aging↗