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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↗
PubMed1982

Modelling perceptual distortion: amplitude and phase transmission in the human visual system.

In this paper we consider the complementary properties of image amplitude and phase components and their role in normal and amblyopic vision. Specific two-dimensional filtered images are included to demonstrate the possible perceptual distortions due to both amplitude and phase disturbances. Finally, the relationships between amplitude and phase filters are discussed with reference to the types of receptive field distributions expected to underly the normal and abnormal cases.

Amblyopia↗
PubMed1981

Insensitivity of peripheral vision to spatial phase.

Tolhurst (1973) had suggested that movement-sensitive mechanisms were the human analogues of transient (Y) neurones in the cat (Enroth-Cugell and Robson 1966) and monkey (Gouras 1968) visual system. We challenged this view in a previous study (Rentschler et al. 1981): in strabismic amblyopia the detection of apparent movement of counterphased gratings is impaired considerably more than pattern detection, whereas no such anomaly is found when the sensitivity to temporal transients is tested. This would imply that with a grating target the detection of lateral movement and of transients is not mediated by the same class of mechanisms. Moreover, we have shown that normal peripheral vision suffers qualitatively from the same kind of movement insensitivity as the amblyopic eye. In this study, we have used a wider range of stimulus parameters to seek more definite evidence.

Humans↗
PubMed1981

Amblyopic abnormality involves neural mechanisms concerned with movement processing.

In strabismic amblyopia the detection of apparent movement for counterphase gratings is considerably more impaired than the detection of pattern. No such anomaly is found for the detection of changes from a blank field when gradual or abrupt onsets or offsets of the temporal grating presentation are used. Similarly, normal peripheral vision is relatively poor in detecting alternation of spatial phase. It is concluded that the observed movement abnormality does not reflect a loss in sensitivity of transient mechanisms but rather a visual insensitivity to spatial phase. This would explain why perceptual distortions and low optotype acuity occur in amblyopes with normal contrast sensitivity.

Amblyopia↗
PubMed1980

Spatial tuning properties in human amblyopia cannot explain the loss of optotype acuity.

Strabismic amblyopes may exhibit in their squinting eye an almost normal contrast sensitivity to gratings although their optotype acuity is strongly impaired. This discrepancy cannot be accounted for by reduced selectivity of spatial-frequency channels or line-sensitivity functions. Alternative explanations for the loss of letter visual acuity as abnormal interactions between psycho-physical detector-mechanisms or defects in spatial phase sensitivity are discussed.

Adult↗
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↗