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Biomedical subjects

R Hilz

Publications and source records attributed to R Hilz.

At least 19 recordsLinked to original sources
PubMed1985

Amblyopic processing of positional information. Part I: Vernier acuity.

Psychometric functions for the recognition of vernier displacements have been measured in 6 strabismic amblyopes, 1 anisometropic amblyope, and 1 bilateral amblyope of unknown aetiology. In the non-amblyopic eyes of the 7 unilateral amblyopes the mean threshold vernier offset was about half of that of a group of 7 experienced normal observers. No correlation was found between vernier acuities and Snellen acuities in the abnormal eyes of squinters. These eyes also displayed massive distortions of horizontal spatial values causing perceptual distortions. In all but one of the amblyopic eyes tested hyperacuity virtually disappeared at the brief exposure duration of 50 ms. None of the observed effects could be predicted from the amblyopic contrast sensitivities, grating resolutions, or letter acuities. This suggests that the loss of positional information is an independent and most significant feature of amblyopic visual dysfunction.

Amblyopia↗
PubMed1983

Discrimination thresholds in the two-dimensional spatial frequency domain.

In two experiments we have determined the discriminability between two sinusoidal gratings as a function of orientation and spatial frequency differences. Twelve orientation (15 degrees steps) and four spatial frequencies (2, 4, 8, 12 c/deg) were considered and corresponding discrimination thresholds were determined. Results indicated that: (a) spatial frequency discrimination thresholds did not significantly vary over all frequency and orientation positions, and averaged at +/- 1/8 octave limits. (b) Orientation thresholds only slightly increased with spatial frequency (from +/- 5 degrees at 2 c/deg to +/- 6 degrees at 12 c/deg). (c) A large and consistent anisotropy occurred with orientation thresholds showing most sensitivity in the horizontal and vertical directions, with largest thresholds at the oblique angles. No oblique effect was observed with spatial frequency thresholds. These results confirm past observations, providing an extensive set of threshold measurements in the two-dimensional spatial domain.

Discrimination, Psychological↗
PubMed1979

Abnormal orientation selectivity in both eyes of strabismic amblyopes.

In normal observers preadaptation to a parallel grating increases the contrast threshold for a line whereas a perpendicular grating has no effect. Such orientation selectivity was not found in the amblyopic eye of two out of five squinters. Only a weak after-effect produced with a grating parallel to the line was obtained in the good eye of four of the amblyopes while all of them show an abnormal threshold reduction following adaptation to a perpendicular grating. This suggests a relationship between abnormal binocular interaction during visual development and the organization of orientational mechanisms but does not explain the loss of visual acuity in amblyopia.

Adaptation, Ocular↗