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PubMed1995

Visual acuity in a population aged 70 years or older; prevalence and causes of visual impairment.

Visual acuity and the prevalence and causes of impaired vision were studied in an epidemiological cross-sectional population study of inhabitants aged 70 years or older in three communities in the county of Oulu, Finland. 500 of the 560 eligible persons (89.3%) were examined. Information on visual acuity was obtained for 476 co-operative persons (85.0%). 59.0% had a visual acuity of 0.3-0.6 in the better eye. 10.1% (48 persons) had low vision and 1.9% (9 persons) were blind as categorized according to the classification of visual impairment by the World Health Organization. Experienced visual capacity did not, however, always correspond to objective tests. Age-related maculopathy and cataract were the leading causes of visual deterioration. Age-related maculopathy was the main cause of low vision and blindness in 4.6% of the population. In 1.3% the etiology was cataract, and in 2.1% both early age-related maculopathy and cataract were present without obvious dominance. Cataract was often associated with other conditions. Glaucoma was considered the main cause of visual deterioration in 1.5%, diabetic maculopathy in 0.6% and macula pucker in 0.4%. In 1.5% the visual deterioration was due to other causes.

Aged↗

PubMed1977

Effect of selective visual interference on visualization.

The extent of visual processing involved in visualizing objects was investigated by the use of selective visual interference. Subjects read concrete words and visualized them. This produced an approximately ten-fold increase in the slope of the latencies of wholistic visualization as a function of set size compared to that when subjects responded after listening to the descriptions of the objects. Males produced significantly steeper slopes than females in both listening and reading conditions, indicating that they find visualization more difficult. It is concluded that the interference on the visualization task was in the main disrupting active visual processing as no spatial manipulation of the objects was required.

Auditory Perception↗

PubMed1998

Relation of visual perception and visual-motor integration for clumsy children.

The purpose of this study was to examine the relationship between visual perception and visual-motor integration in 30 normal children compared to 30 clumsy children. Difficulty in visual perception, as assessed by the Test of Visual-Perceptual Skills, accounts for about half the variance in the clumsy children's performance in visual-motor integration, as assessed by the Developmental Test of Visual Motor Integration. In contrast, the correlation between scores on these tests for normal control children was low and not significant. These results suggest that visual perception and visual-motor integration may be separate functions in normally developing children. When considering clumsy children, however, these functions cannot be considered as two independent skills.

Child↗

PubMed2005

Spatial versus object visualizers: a new characterization of visual cognitive style.

The visual system processes object properties (such as shape and color) and spatial properties (such as location and spatial relations) in distinct systems, and neuropsychological evidence reveals that mental imagery respects this distinction. The findings reported in this article demonstrate that verbalizers typically perform at an intermediate level on imagery tasks, whereas visualizers can be divided into two groups. Specifically, scores on spatial and object imagery tasks, along with a visualizer-verbalizer cognitive style questionnaire, identified a group of visualizers who scored poorly on spatial imagery tasks but excelled on object imagery tasks. In contrast, a second group of visualizers scored high on spatial imagery tasks but poorly on object imagery tasks. The results also indicate that object visualizers encode and process images holistically, as a single perceptual unit, whereas spatial visualizers generate and process images analytically, part by part. In addition, we found that scientists and engineers excel in spatial imagery and prefer spatial strategies, whereas visual artists excel in object imagery and prefer object-based strategies.

Adolescent↗

PubMed1981

Layer-specific labelling of cat visual cortex after stimulation with visual noise: a [3H]2-deoxy-d-glucose study.

Tritiated 2-deoxy-D-glucose (2-DG) was used to demonstrate layer specific uptake of 2-DG at the cellular level in the visual cortex of the cat after stimulation with different kinds of visual stimuli. Two-dimensional static Gaussian visual noise drifting across the visual field led to an increased accumulation of 2-DG in layers III and V as compared to the amount of radioactivity in layer IV. In unstimulated control tissue of visual cortex a homogeneous pattern of labelling was found. Horizontal bars moving vertically across the visual field increased the uptake in layer IV more than in all other layers. Analysis of the 2-DG uptake at the cellular level revealed that visual noise activated two bands of cells, one above and one below layer IV, whereas bar stimuli activated cells mainly in layer IV. Accumulation of 2-DG was always higher in the perikarya than in the surrounding neuropil. These results confirm the physiologically recorded properties of cells in different cortical layers.

Animals↗

PubMed1994

Visual hemispheric dominance induced in split brain cats during development: a model of deficient interhemispheric transfer derived from physiological evidence in single visual cortex cells.

The effects of cancellation of both interhemispheric callosal transfer and interocular interactions, were studied in early monocularly deprived cats. The main purpose of this study was therefore to prove whether unilateral hemispheric dominance would result under these conditions and to what extent each hemisphere will be functionally independent. Secondly, we have attempted to establish such an experimental model physiologically, on the single cell level. Interhemispheric transfer was surgically canceled by sagittal transection of the corpus callosum. In addition, the ocular projections were separated by sagittal transection of the optic chiasm in the transbuccal approach. This condition had practically induced visual split brain condition in these cats. These manipulations were carried out concurrently with monocular deprivation (SBDK group) which was surgically done by eye closure during the critical period of development of the visual system. Thus, the hemisphere ipsilaterally to the visually deprived eye had developed under conditions of deficient visual experience while the hemisphere ipsilaterally to the normal eye had developed under conditions of unaltered visual experience. A group of cats (SBK) similarly operated but equally binocularly exposed during development was served as controls. In addition, adult cats similarly operated during adulthood either chronically or acutely were studied to evaluate the effects of interhemispheric and interocular separation. Other groups of cats were also studied for comparison, and included sham operated and normal adult cats. At adulthood, electrophysiological studies were done on these cats, in which action potentials were extracellularly recorded from single cells in the visual cortex (area 17-18 boundary) following anesthesia and paralysis. Stimulation was carried out manually and by a computer driven optical system, presenting on a tangent screen light bars at various spatial positions, orientations and directions. Receptive fields were thus mapped for all neurons and their dimensions and eccentricities were measured. The responsiveness, ocular dominance and other parameters were also studied for these cells. The results in the early deprived cats and in their controls, had shown a full separation between the two hemispheres, as reflected in the almost absolute ipsilateral eye responsiveness (> 97.0% cells). In comparison, in the sham operated and in the normal control cats only minor proportions of cells (13.0-18.7%) have been found as ipsilaterally and monocularly driven, showing almost full interhemispheric and interocular interaction. The main difference, however, in the results between the early monocularly deprived cats and their controls is that in the first group the two hemispheres were asymmetric concerning the amount of visual activation and in the second one they were very symmetric.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2000

Dynamic topography of pattern visual evoked potentials (PVEP) in psychogenic visual loss patients.

We investigated to measure the objective visual acuity using pattern visual evoked potentials (PVEP) to help the diagnosis with psychogenic visual loss (PVL) who ranged in age from 7 to 14 years old. Pattern stimuli consisted of black and white checkerboard patterns (39, 26, 15 and 9') with a visual angle of 8 degrees and a contrast level of 15%. The pattern reversal frequency was 0.7 Hz. This resulted in an average of 100 PVEP per session. Visual acuity of 0.1 was consistent with the 39' pattern, 0.2 with the 26' pattern, 0.5 with the 15' pattern, and 1.0 with the 9' pattern. As the results, five PVL patients could measure visual acuity with this method in the present study. The PVEP is useful in evaluating the visual acuity and helped to diagnose the PVL patients. In addition we used the dynamic topography to study the difference in the results of the PVEP. The dynamic topography obtained from the results of the PVEP was analyzed. The flow type of the P100 component diverged into three types (separated type, hollow type and localized type) in the PVL patients and the normal children. The localized type was observed in 59.1% of normal children and in 56.3% of PVL patients. While the separated type was shown in 6.8% of normal children and in 8.3% of PVL patients. There were not significant differences between the PVL patients and the normal children in each type.

Adolescent↗

PubMed2002

Language-specific tuning of visual cortex? Functional properties of the Visual Word Form Area.

The first steps in the process of reading a printed word belong to the domain of visual object perception. They culminate in a representation of letter strings as an ordered set of abstract letter identities, a representation known as the Visual Word Form (VWF). Brain lesions in patients with pure alexia and functional imaging data suggest that the VWF is subtended by a restricted patch of left-hemispheric fusiform cortex, which is reproducibly activated during reading. In order to determine whether the operation of this Visual Word Form Area (VWFA) depends exclusively on the visual features of stimuli, or is influenced by language-dependent parameters, brain activations induced by words, consonant strings and chequerboards were compared in normal subjects using functional MRI (fMRI). Stimuli were presented in the left or right visual hemifield. The VWFA was identified in both a blocked-design experiment and an event-related experiment as a left-hemispheric inferotemporal area showing a stronger activation to alphabetic strings than to chequerboards, and invariant for the spatial location of stimuli. In both experiments, stronger activations of the VWFA to words than to strings of consonants were observed. Considering that the VWFA is equally activated by real words and by readable pseudowords, this result demonstrates that the VWFA is initially plastic and becomes attuned to the orthographic regularities that constrain letter combination during the acquisition of literacy. Additionally, the use of split-field stimulation shed some light on the cerebral bases of the classical right visual field (RVF) advantage in reading. A left occipital extrastriate area was found to be activated by RVF letter strings more than by chequerboards, while no symmetrical region was observed in the right hemisphere. Moreover, activations in the precuneus and the left thalamus were observed when subjects were reading RVF versus left visual field (LVF) words, and are likely to reflect the attentional component of the RVF advantage.

Adult↗

PubMed2004

Effects of visual contrast on visual evoked potentials and Doppler signal.

We studied visually evoked cerebral blood flow responses (VEFR) and visual evoked potentials (VEP) to different visual contrasts and analysed the relationship between them. The records were made from 35 healthy volunteers aged 38.6 +/- 10.1 years. The stimulus was a black-and-white checkerboard with visual contrasts (VC) of 1%, 10% and 100%. The VEFR were measured in the posterior cerebral artery using transcranial Doppler, and the VEP were recorded from the occipital leads. We found the relationship between visual contrast and VEFR (r = 0.79, P < 0.01) as well as between visual contrast and VEP (r = 0.71, P < 0.01). We also found moderate association between the VEP and the VEFR (r = 0.69, P < 0.01). The analysis of the regression slopes between two different age subgroups (P < 0.01) did not show a significant difference (P = 0.020). We concluded that a simultaneous recording of VEFR and VEP to visual contrasts could allow an assessment of neurovascular coupling in humans.

Adult↗

PubMed1994

Patterned light flash evoked short latency activity in the visual system of visually normal and in amblyopic subjects.

In a previous experimental study on anaesthetized cat it was shown that a short latency (35-40 ms) cortical potential changed polarity due to the presence or absence of a pattern in the flash stimulus. The results suggested one pathway of neuronal activation in the cortex to a pattern that was within the level of resolution and another to patterns that were not. It was implied that a similar difference in impulse transmission to pattern and non-pattern stimuli may be recorded in humans. The present paper describes recordings of the short-latency visual evoked response to varying light flash checkerboard pattern stimuli of high intensity in visually normal and amblyopic children and adults. When stimulating the normal eye a visual evoked response potential with a peak latency between 35 to 40 ms showed a polarity change to patterned compared to non-patterned stimulation. The visual evoked response resolution limit could be correlated to a visual acuity of 0.5 and below. In amblyopic eyes the shift in polarity was recorded at the acuity limit level. The latency of the pattern depending potential was increased in patients with amblyopia compared to normal, but not directly related to amblyopic degree. It is concluded that the short latency, visual evoked response that mainly represents the retino-geniculo-cortical activation may be used to estimate visual resolution below 0.5 in acuity level.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1975

Responses to visual stimulation and relationship between visual, auditory, and somatosensory inputs in mouse superior colliculus.

The superior colliculus was studied in anesthetized mice by recording from single cells and from unit clusters. The topographic representation of the visual filed was similar to what has been found in other mammals, with the temporal part of the contralateral visual field projecting posteriorly and the inferior visual field projecting laterally. At the anterior margin of the tectum receptive fields recorded through the contralateral eye and invaded the ipsilateral visual hemifield for up to 35 degrees, suggesting that the entire visual field through one eye is represented on the contralateral superior colliculus. Cells located closest to the tectal surface had relatively small receptive fields, averaging 9 degrees in center diameter; field sizes increased steadily with depth. The prevailing cell type in the stratum zonal and superficial gray responded best to a small dark or light object of any shape moved slowly through the receptive-field center or to turning a small stationary spot on or off. Large objects or diffuse light were usually much less effective. Less than one-quarter of superficial layer cells showed directional selectivity to a moving object, the majority of these favoring up and nasal movement. The chief visual cell type in the stratum opticum and upper part of the intermediate gray resembled in the newness neurons described for many other vertebrates: they had large receptive fields and responded best to up and nasal movement of a small dark or light object, whose optimal size was similar to the optimum for upper-layer cells. If the same part of the receptive field was repeatedly stimulated there was a marked tendency to habituate. Only very few cels responded to the ipsilateral eye. Intermixed with visual cells in the upper part of the intermediate gray were cells that responded to somatosensory or auditory stimuli. Here bimodal and trimodal cells were also seen. In deeper layers somatosensory and auditory modalities tended to take over. These two modalities were not segregated into sublayers but rather seemed to be arranged in clusters. Responses to somatosensory and auditory stimuli were brisk, showing little habituation to repeated stimulation.

Acoustic Stimulation↗

PubMed2001

Experience-dependent visual cue integration based on consistencies between visual and haptic percepts.

We study the hypothesis that observers can use haptic percepts as a standard against which the relative reliabilities of visual cues can be judged, and that these reliabilities determine how observers combine depth information provided by these cues. Using a novel visuo-haptic virtual reality environment, subjects viewed and grasped virtual objects. In Experiment 1, subjects were trained under motion relevant conditions, during which haptic and visual motion cues were consistent whereas haptic and visual texture cues were uncorrelated, and texture relevant conditions, during which haptic and texture cues were consistent whereas haptic and motion cues were uncorrelated. Subjects relied more on the motion cue after motion relevant training than after texture relevant training, and more on the texture cue after texture relevant training than after motion relevant training. Experiment 2 studied whether or not subjects could adapt their visual cue combination strategies in a context-dependent manner based on context-dependent consistencies between haptic and visual cues. Subjects successfully learned two cue combination strategies in parallel, and correctly applied each strategy in its appropriate context. Experiment 3, which was similar to Experiment 1 except that it used a more naturalistic experimental task, yielded the same pattern of results as Experiment 1 indicating that the findings do not depend on the precise nature of the experimental task. Overall, the results suggest that observers can involuntarily compare visual and haptic percepts in order to evaluate the relative reliabilities of visual cues, and that these reliabilities determine how cues are combined during three-dimensional visual perception.

Cues↗

PubMed1993

Benefit from visual cues in auditory-visual speech recognition by middle-aged and elderly persons.

The benefit derived from visual cues in auditory-visual speech recognition and patterns of auditory and visual consonant confusions were compared for 20 middle-aged and 20 elderly men who were moderately to severely hearing impaired. Consonant-vowel nonsense syllables and CID sentences were presented to the subjects under auditory-only, visual-only, and auditory-visual test conditions. Benefit was defined as the difference between the scores in the auditory-only and auditory-visual conditions. The results revealed that the middle-aged and elderly subjects obtained similar benefit from visual cues in auditory-visual speech recognition. Further, patterns of consonant confusions were similar for the two groups.

Acoustic Stimulation↗

PubMed1990

Visually guided behavior of monkeys after early binocular visual deprivation.

Four infant monkeys were binocularly deprived of vision through their first year of life. After the end of the deprivation their visually guided behavior was followed for one year. Behavioral tests were performed to assess their visual functions. The performance of the deprived monkeys was compared with the performance of three normally sighted monkeys. The following functions were tested: the monkey's ability to detect a moving light spot, to track a moving object, to grasp an object, to chatter the teeth in response to a threatening face, to pick pellets from a board, to respond to a sudden visual threat and to move about in a wide space. The visually deprived monkeys remained severely visually handicapped. They were able to detect a moving light spot in a darkened room and to recognize the movement of large objects. However, they continued bumping into objects and used tactile exploration when moving about in a wide space. They never learned to respond to a threatening face, which for a normal monkey is part of the normal behavioral repertoires. The persistently poor visually guided behavior of these monkeys is in agreement with the electrophysiological findings in the posterior parietal association cortex of these monkeys; early visual deprivation permanently reduces the number of visually responsive cell groups in this association area.

Animals↗

PubMed2000

Training ameliorates deficits in visual detection and orienting following lesions of primary visual cortex sustained in adulthood and in infancy.

Purpose: Damage of primary visual cortex in adult humans, monkeys and cats severely disrupts vision by disconnecting much of the cogni-tive processing machinery of extrastriate cortex from its source of visual signals in the retina. Equivalent lesions sustained early in life result in partial sparing of visual processing functions and evidence from the mature brain suggests that systematic training procedures can ameliorate the impact of remaining deficits. The purpose of the present work was to use two reflex-based, visual detection and orienting tasks to test for the therapeutic effects of reha-bilitative training in cats that sustained lesions of primary cortical areas 17 & 18 in adulthood, and to test whether similar training is of benefit to cats that incurred equivalent lesions at one month-of-age (P28) or shortly after birth (P1). Methods: Cats were trained to attend to static visual and auditory cynosures and tested on their ability to disengage the cynosure and orient towards a target presented in the periphery of the testing arena. Targets were: 1) a high contrast, dark, moved rod; 2) an illuminated static light-emitting diode (LED); and 3) a broad band, white noise, sound stimulus. Results: On Task 1, cats with lesions of areas 17 & 18 sustained in adulthood are markedly impaired whereas cats that sustained lesions in infancy exhibit partial sparing of the visual operations underlying this task. With training, the performance of all cats improved. On Task 2, performance by the adult-lesion and the P1-groups were markedly impaired, whereas the P28-group exhibited partial sparing. On Task 3, per-formance by all groups was uniformly high. No detectable benefits of training were identified on tasks 2 and 3. Conclusions: Overall, the results show that cats incur definite benefits of training following visual cortex lesions regardless of whether the lesions were sustained early in life or later, but the benefits are limited to specific types of visual stimuli.

Journal Article↗

PubMedDate not supplied

Poor visual discrimination and visual hallucinations in Parkinson's disease.

This study examined the relationship between deficits in color and contrast discrimination and visual hallucinations (VH) in patients with Parkinson's disease (PD) and normal visual acuity. Thirty-five nondemented and nonpsychotic PD patients with normal visual acuity and without major ophthalmologic disease were interviewed twice and divided into two groups: hallucinators (n = 14) and non-hallucinating controls (n = 21). The groups were compared for color vision (assessed by Lanthony D-15 [LD] and Farnsworth-Munsell 100 hue [FM] tests), and for contrast sensitivity (tested by Vis tech tables [VT] and monocular and binocular Pelli-Robson test [PR]). There was no difference in age, duration or stage of PD, or dosage or duration of levodopa therapy between the two groups. Parkinson's disease patients showed impairment on all visual tests, with the hallucinators performing worse than the controls on all tests. This difference was significant for the LD (p < 0.007), the VT at 1.5 and 3 cycles per degree (p < 0.037 and 0.043, respectively) and the monocular PR tests (p < 0.049). The results led the authors to conclude that in patients with normal visual acuity, those with VH show added visual deficits of color and contrast discrimination. These ophthalmopathies may therefore be facilitating factors for visual hallucinations in PD and justify more focused research on the pathophysiology of visual hallucinations in Parkinson's disease.

Aged↗

PubMed1987

Visual loss in pseudotumor cerebri. Incidence and defects related to visual field strategy.

Visual field examinations were performed serially on 20 patients with pseudotumor cerebri using a modified Armaly-Drance visual field strategy with a Goldmann perimeter as well as an automated perimeter (Octopus). Visual loss was found in 75% of eyes using the manual strategy and in 77.5% of eyes with automated threshold perimetry. This incidence of visual loss is 50% greater than any previously reported series. All major defects detected were present with both types of perimetry. Both strategies were more sensitive for documenting visual loss than previously described strategies. Since therapy for pseudotumor cerebri is determined by the degree and progression of visual loss, a specific sensitive strategy, rather than routine screening perimetry, should be used for determination of visual loss.

Adult↗

PubMed1992

Comparison of preoperative 10-Hz visual evoked potentials to contrast sensitivity and visual acuity after cataract extraction.

Cataract patients whose surgical outcomes were in question were referred for testing by visual evoked potentials, elicited through closed eyelids by a luminance stimulus (flash) that appeared 10 times per second. Visual evoked potentials were rated as normal (predicted acuity of 20/50 or better) or abnormal (predicted acuity of 20/60 or worse). Postoperative Arden and Optronix contrast sensitivities and visual acuities were determined in 37 patients who had no intraoperative or early postoperative complications. Arden grating scores of less than 100 were rated as normal. The optimal and cutoff spatial frequency values were determined for the Optronix scores. Optimal and cutoff values of greater or equal to 1 c/deg and 12 c/deg, respectively, were rated as normal. Visual acuities were considered normal at 20/50 or better. Preoperative visual evoked potentials were quantitatively compared to the postoperative contrast sensitivities and visual acuities by 2 x 2 contingency tables. The accuracy of prediction was 79% for the visual acuities, 62% for the Optronix optimal values, 70% for the Optronix cutoff values and 62% for the Arden gratings.

Aged↗