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Biomedical subjects

S A Wurst

Publications and source records attributed to S A Wurst.

5 recordsLinked to original sources
PubMed1990

Binocular advantage and visual processing in dyslexic and control children as measured by visual evoked potentials.

The role of visual processing in dyslexia continues to stir controversy. Previous research using early components of visual evoked potentials (VEP's) has revealed differences in visual processing between dyslexics and controls. VEP's have successfully indexed binocular advantage. Intrasensory functioning could conceivably be deficient in dyslexics. This study recorded VEP's in response to contrast-reversing checkerboards binocularly and monocularly from dyslexic and control children. The overall monocular and binocular amplitudes of the major positive peaks (P100) were greater for controls than dyslexics; however, contrary to the original hypothesis, the magnitude of binocular advantage was higher for dyslexics than for the control children. Stimulus factors had an effect, but did not interact with reading ability.

Analysis of Variance↗
PubMed1990

Age and binocular advantage: A VEP assessment.

Monocular and binocular visual evoked potentials (VEP's) were recorded in response to contrast-reversing checkerboard patterns of 2 check sizes (14 and 28 min arc) and 2 contrast-reversal rates (1.88 and 7.50 rps) in children (10 and 11-year-olds) and young adults (20 to 30-year-olds). The magnitude of binocular advantage, expressed as the ratio of the binocular to the average monocular response, was assessed by amplitude measurements of the major positive peak. The overall VEP amplitudes were larger for children than for adults across all conditions. The VEP amplitudes for binocularly viewed patterns were also consistently larger than the VEP amplitudes for the monocularly viewed patterns for both age groups. However, when the binocular advantage was expressed as a ratio of binocular to monocular average (MAV), the amplitude difference between the age groups was no longer apparent; although the children's average VEP responses were of a larger amplitude, the binocular advantage remained the same regardless of age.

Adult↗
PubMed1986

Tradeoffs between stereopsis and proximity luminance covariance as determinants of perceived 3D structure.

A 2D polar projection of a 3D wire cube (Necker cube) in clockwise rotation can be perceived either veridically as a clockwise-rotating cube (rigid percept) or as a counterclockwise-rotating rubbery, truncated pyramid (nonrigid percept). The 3D percept is influenced by various cues: linear perspective, stereo disparity, and proximity-luminance covariance (PLC, the intensification of edges in proportion to their proximity to the observer). Perspective, by itself or in combination, is a very weak cue whereas PLC is a powerful cue [Schwartz and Sperling (1983) Bull. Psychon. Soc. 21, 456-458]. Here we determined psychometric functions for perceptual resolution in static displays and dynamic rotating displays (with and without a static preview) as determined by stereopsis and PLC in isolation and with both cues jointly, possibly in conflict. Stereopsis was the dominant cue in static displays and in most dynamic displays. When a static display preceded a dynamic display, it strongly influenced the subsequent dynamic percept. Perceptual resolution in all conditions was accurately described by a winner-take-all model in which the strength of evidence for each percept from different cues is simply algebraically added.

Depth Perception↗
PubMed1984

Complexity effects on reaction-time measures of visual persistence: evidence for peripheral and central contributions.

Two experiments are presented that attempt to determine the effect of operationally defined stimulus complexity on visual persistence. Two common measures of complexity are employed in both experiments. In Experiment 1, visual persistence for high-contrast, solid black figures increases with increasing target duration and with decreasing complexity. In Experiment 2, which uses outline figures of the same sizes and shapes as in the first experiment, visual persistence increases both with increasing target duration and with increasing complexity. It is proposed that the very different results from the two experiments may reflect the separate functioning of a visible, sensory persistence and a higher order, schematic persistence. The reaction-time (RT) measure of persistence that was employed may be sensitive to either of these persistences, depending upon stimulus and task conditions. Implications are suggested for (a) the importance of sensory processes in some manipulations of target complexity and (b) the possible role of peripheral and central factors in visual persistence.

Adult↗