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↗

PubMed1982

Analysis and restitution of visual function in a case of cerebral amblyopia.

In a patient suffering from a severe bilateral dysfunction in both occipital and parietal areas we have found: (1) A loss of contrast-sensitivity, being strongest in the range of spatial frequencies where the normal eye is most sensitive; (2) Virtually normal grating resolution, a severe loss in letter acuity (about 15-fold), and a very strong loss in vernier acuity (about 100-fold); (3) Rapid partial recovery of contrast sensitivity due to stimulation; (4) Slow partial recovery of letter acuity due to CAM rotating grating treatment; (5) No improvement of a 10-fold temporal retardation in the speed of reading. Evidence is presented that the residual impairment of vision depends upon improper synthesis of spatial frequency components originating from a heavy loss in processing speed and abnormally long store duration for high spatial frequency information.

Adult↗

PubMed1981

Illusions of filled lateral and angular extent. The role of cortical feature detectors.

The common principle of the illusions found by Helmholtz and Botti is the overestimation of a filled extent. They differ in that Helmholtz's illusions of filled angular extent can be accounted for in terms of spatial two-line interactions, whereas Botti's illusions of filled lateral extent cannot. The former observation is consistent with the assumption of interacting orientation-detectors in the visual cortex. The Botti illusion probably depends on global computation in the visual system.

Humans↗

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↗

PubMed1979

Spatial probability summation and disinhibition in psychophysically measured line-spread functions.

Explore the source record for details and available documents.

Form Perception↗

PubMed1978

Accuracy of evoked potential refractometry using bar gratings.

We recorded cortical potentials evoked by phase-alternating square-wave gratings. Significant effects of varying the refractive power of the eye are obtained only at 5 cycles/degree (cy/deg) and above. The extrapolation to zero amplitude of the evoked response as a function of spatial frequency predicts the psychophysical visual acuity even for the myopic eye. As the sensitivity of meridional refraction using sufficiently fine bar gratings is better than 0.5 D it provides a suitable means for the measurement of astigmatism.

Astigmatism↗

PubMed1977