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At least 1,639 records · Page 91Linked to original sources
PubMed1990

Prism adaptation and viewing distance.

Previous studies have shown that subjects with normal binocular vision adapt to prism-induced phorias. However, there are conflicting reports as to the amount of adaptation shown to horizontal prisms. Some investigations found a greater amount of adaptation to base out prisms compared with base in, whilst others found the reverse and one study found no adaptation to base out prism at all. This study investigated the adaptation response to horizontal prisms at distance and near in a larger number of subjects (n = 40). The results confirmed our previous findings and showed that at distance the adaptation responses are asymmetrical, there being a significantly greater amount of adaptation to base out prism compared with base in, whilst at near the responses are virtually symmetrical. Possible reasons for these findings are discussed.

Adaptation, Ocular↗
PubMed1989

Understanding collision dynamics.

In two experiments we investigated people's ability to judge the relative mass of two objects involved in a collision. It was found that judgments of relative mass were made on the basis of two heuristics. Roughly stated, these heuristics were (a) an object that ricochets backward upon impact is less massive than the object that it hit, and (b) faster moving objects are less massive. A heuristic model of judgment is proposed that postulates that different sources of information in any event may have different levels of salience for observers and that heuristic access is controlled by the rank ordering of salience. It was found that observers ranked dissimilarity in mass on the basis of the relative salience of angle and velocity information and not proportionally to the distal mass ratio. This heuristic model was contrasted with the notion that people can veridically extract dynamic properties of motion events when the kinematic data are sufficient for their specification.

Acceleration↗
PubMed1989

[Rest position of the eyes and its effect on viewing distance and visual fatigue in computer display work].

A deviation between the angle of convergence during visual work and the resting level of the vergence system (vergence discrepancy) should be associated with costs; subjects should tend to reduce these costs by increasing the observation distance. The remaining costs should contribute to visual fatigue. Both hypotheses were tested using a sample of 40 subjects, mainly students. In agreement with the first hypothesis, subjects with large initial vergence discrepancy increased their observation distance more in the course of 1 1/2 hours of visual work than subjects with smaller initial vergence discrepancy. Visual fatigue was assessed using a set of questions developed in two pilot studies. Contrary to the second hypothesis, visual fatigue did not depend on effective vergence discrepancy, that is, the deviation between the resting level of the vergence system and the actual angle of convergence. In addition, such a relationship was not found for further dependent variables (performance, BMS questionnaire, critical flicker frequency, evaluation of conditions of work, postural complaints). The results are discussed with respect to the role of tonic and dynamic components of the vergence system for visual fatigue.

Adult↗
PubMed1989

The effect of high frequency flicker on accommodation.

Monocular accommodation was measured by a laser optometer while two subjects viewed a letter matrix target illuminated by steady or intermittent (300, 100, 50 and 25 Hz) light and presented at a number of optical distances (0.5, 1.5, 2.5, 3.5 and 4.5 D). At certain rates of intermittent illumination, both above (50 Hz) and below (25 Hz) flicker fusion, an increased accommodation response was found. This increase occurred at all optical distances, except for the distance closest to each subject's dark focus, and resulted in a more accurate accommodation response for one subject, and a less accurate one for the other. Furthermore, for both subjects, evidence of an increase in the amplitude of the fluctuations in accommodation at 50 and 25 Hz was found for the higher stimulus levels. The implications of these findings for the control of accommodation and for practical problems of visual performance in the environment, such as visual discomfort associated with fluorescent lighting and intermittently illuminated visual display units, are discussed.

Accommodation, Ocular↗
PubMed1989

Intelligence as a correlate of children's problem solving.

Previous work on children's problem solving was extended by directly comparing the strategies of intellectually gifted, average, and mentally retarded children on 2 two-dimensional integration problems--the balance scale and inclined plane. Comparisons of the distributions of strategies for each group showed that most gifted children integrated dimensional information by addition and many average children used lexicographic strategies. Mentally retarded children relied on a single dimension of the balance scale, but they were more likely to use lexicographic strategies for the inclined plane. Possible explanations for the large number of unclassified mentally retarded children were discussed.

Adolescent↗
PubMedDate not supplied

[Estimation by toads of the distance to the moving objects and their true size: neuroethological and comparative aspects].

In two sets of experiments, studies have been made on the parameters by which the toad Bufo bufo estimates the neighbour and remote moving objects. In absence of the structural surrounding, a dark target with a diameter 17.2 degrees (3 cm at a distance of 10 cm) and with the rate of movement 36, 72 and 145 degrees/sec evoked in toads only feeding turns; at the rates 72 and 145 degrees/sec, together with these turns, animals usually fired with their tongues to the direction of the target, revealing evident underestimation of the distance and real size of the object. Under the same experimental conditions, a target with a diameter 1.2 degrees (0.25 cm at a distance of 12 cm) and the rate of movement 0.6 and 3 degrees/sec produced mainly frightful reaction, which indicates overestimation of the distance to the object and its size. The same object moving at a structural background evoked only feeding reactions, i.e. the animals correctly estimated the distance to the target and its size.

Animals↗
PubMed1988

Potential range of clear vision in monovision.

A possible limitation for monovision contact lens treatment of presbyopia is that an intermediate correction cannot be incorporated into the prescription without compromising distance or near vision. A simple model using a standard prescription strategy for the add and a conservative estimate for the static depth of focus of the eye was used to predict the range of clear vision with monovision lenses. For adds up to 2D, little compromise in visual acuity was predicted for any gaze position.

Accommodation, Ocular↗
PubMed1988

Memory for the locations of pictures: evidence for hierarchical clustering.

The role of similarity in memory for location of pictures was examined. Undergraduates memorized the locations of 10 pictures situated within a map. The similarity of the pictures was manipulated. Two days later, subjects were tested for their memory of the locations. The results indicated that subjects clustered the locations of the pictures on the basis of pictorial similarity, such that locations of similar pictures were judged as closer than equidistant locations of dissimilar pictures. The results are discussed in the framework of a hierarchical model of spatial memory.

Cognition↗
PubMed1978

[Drawings by patients with unilateral visuospatial agnosia].

Drawings made by 25 patients with neurosurgical diseases causing focal lesions in the posterior areas of the right, not dominant cerebral hemisphere due to expanding changes. Experimental clinical investigations by the method of Luria demonstrated in these cases presence of left-sided visuospatial agnosia. The material was analysed from the point of view of the features of drawings characteristic for the syndrome of disturbances and the localizatory and diagnostic value of drawings. Characteristic disturbances of drawings and their placement were observed suggesting that the patients ignored the left half of the visual space due to damage to the right parieto-occipital non-dominant cerebral hemisphere. The drawing test is regarded as a valuable method for the diagnosis and localization of lesions in the neurological and neuropsychological practice.

Agnosia↗
PubMed1986

Characteristics of exodeviations: I. A comparison of three classes.

A retrospective study of 179 patients (69 males and 110 females) with binocular visual dysfunction and an exodeviation at distance or near or at both distances has been completed. The mean age of 19.7 years was significantly younger than the population from which they were referred. The patients were classed as convergence insufficiency, equal exodeviation, or divergence excess, based on the relation of the distance and near angles of deviation. Based on these criteria, interaction was found to be present between the diagnostic class and the frequency of the deviation, the symptoms reported, and a variety of clinical parameters such as the angles of deviation at distance and near, the AC/A ratio, positive and negative vergence values, the amplitude of accommodation, and the threshold of stereopsis. A number of statistical relations were noted between the frequency of the deviation vs. the symptoms reported and a variety of the clinical parameters. The implications of these results are discussed.

Accommodation, Ocular↗
PubMed1986

Characteristics of exodeviations: II. Changes with treatment with orthoptics.

This study examined retrospectively the records of 179 patients who had binocular visual dysfunction as a result of an exodeviation (either at distance or near or both). The patients were classified as having convergence insufficiency (N = 110), equal exodeviations (N = 49), or divergence excess (N = 18). The diagnostic groups and the different frequencies of deviation reacted differently to treatment with a standard orthoptic regimen. Nearly all the patients (97%) achieved some improvement in either objective or subjective areas or both. However, fewer were able to satisfy the criteria set for total success. Factors correlated with the success of the treatment were the initial angle of deviation at distance and the initial level of stereopsis. The results and implications of this study are discussed.

Adolescent↗
PubMed1986

Blind spot "fixation" in normal eyes: implications for eccentric viewing in bilateral macular disease.

Normal subjects were trained to look to the side of a small, flickering target in order to make this target disappear within the physiological blind spot of the right eye. Subsequently, subjects aimed the eye more eccentrically when the target was nearer and less eccentrically when the target was farther than when it was at the training distance of 1.5 m. Thus, the eccentric eye aiming of our subjects represented a compromise between looking to the side of the target by a constant visual angle and by a constant lateral extent. We propose that patients who lose central vision bilaterally may similarly err in trying to aim the diseased macula to one side of targets by a constant visual angle, impeding their ability to use a single, nonfoveal region effectively.

Distance Perception↗