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Biomedical subjects

R S Harwerth

Publications and source records attributed to R S Harwerth.

99 records · Page 6Linked to original sources
PubMed1978

A sensory mechanism for amblyopia: electrophysiological studies.

Steady-state visual evoked potentials were elicited by the appearance/disappearance of sinusoidal gratings of varying spatial frequency for both eyes of amblyopic subjects at temporal frequences from 2--32 Hz. The amblyopic eyes showed reduced responses relative to those of the nonamblyopic eyes across a wide range of spatial frequencies, the difference between the 2 eyes being most marked for high spatial frequencies and low temporal frequencies. Both the nonamblyopic and the amblyopic eyes showed a linear relation between the evoked potential amplitude and the logarithm of the stimulus contrast; however, the slope of the line was flatter for the amblyopic eyes. Possible neural mechanisms for the amblyopic eyes' reduced responses to spatial contrast are considered.

Adolescent↗
PubMed1978

Contrast evoked potentials in strabismic and anisometropic amblyopia.

Steady-state visual evoked potentials were elicited by the appearance/disappearance of sinusoidal gratings of varying spatial frequency for both eyes of amblyopic subjects. The amblyopic eyes showed reduced responses and a phase shift relative to the nonamblyopic eyes across a wide range of spatial frequencies. Both the nonamblyopic and amblyopic eyes showed a linear relationship between the evoked potential amplitude and the logarithm of the stimulus contrast; however, the slope of the line was flatter for the amblyopic eyes.

Adolescent↗
PubMed1977

Viewing time and stereoscopic threshold with random-dot stereograms.

The effect of viewing time on the threshold for depth and form discrimination using random-dot stereograms has been investigated. For 12 subjects the relation between logarithm of threshold disparity and logarithm of viewing time was linear for both depth and form discrimination, but the threshold for form discrimination was approximately twice the threshold for depth discrimination. Stereo thresholds determined with random-dot stereograms were not significantly related to stereo thresholds measured with a Howard-Dolman apparatus.

Depth Perception↗
PubMed1977

Spatio-temporal interactions in anisometropic and strabismic amblyopia.

Contrast sensitivity functions for sinusoidal gratings of different spatial frequencies and stimulus durations have been determined for both eyes of amblyopic subjects. For both long and short stimulus durations, the entire contrast sensitivity function of the amblyopic eyes is lower than that of the nonamblyopic eyes. When the gratings were flickered at 10 Hz, the sensitivity for pattern and flicker detection were similar for both eyes at low spatial frequencies. Possible neural mechanisms for the differences in contrast sensitivity are considered with respect to recent psychophysical and electrophysiological evidence for channels with different spatio-temporal properties in the mammalian visual system.

Adult↗
PubMed1975

Pattern and depth discrimination from random dot stereograms.

The discrimination of depth and pattern was investigated using random dot stereograms. For all four subjects, the psychometric function for depth judgments (probability of correct response) was clearly superior to pattern judgments over a range of ten crossed or uncrossed binocular disparity values. Degrading the visual images, either monocularly or binocularly, with various convex lens power (fogging lenses) reduced both depth and pattern discrimination across all disparity values, rather than simply increasing the thresholds. The results are discussed with reference to current theories of stereopsis, and the question of the hierarchial processing of depth and pattern information is considered.

Animals↗
PubMed1971

Prolonged color blindness induced by intense spectral lights in rhesus monkeys.

Prolonged exposure of rhesus monkeys to intense blue light produces long-term changes which are consistent with loss of response of those cones that contain a photopigment with peak absorption at 445 nanometers. The 90 percent reduction of spectral sensitivity in the blue region has lasted more than 5 months. Reduced sensitivity to long wavelengths is produced by adaptation to light of 520 nanometers. This reduced sensitivity, which lasts no more than 30 days, is attributed to a temporary loss of response of the cones containing a photopigment with peak absorption at 535 nanometers.

Animals↗
PubMed1971

Red-green cone interactions in the increment-threshold spectral sensitivity of primates.

Threshold spectral sensitivity of primate eyes is the upper envelope of the sensitivity of three response channels. Sensitivity in the green and red channels is modeled as linear difference functions reflecting neural interaction between cones containing photopigments with 535- and 575-nanometer peaks. Sensitivity in the blue channel seems determined by a single class of cones containing a 445-nanometer photopigment.

Adaptation, Ocular↗