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J Siderov

Publications and source records attributed to J Siderov.

28 records · Page 2Linked to original sources
PubMed1993

Effects of the spatial frequency of test and reference stimuli on stereo-thresholds.

The perceived depth of adjacent regions of stereoscopic stimuli may be influenced, in part, by differences in the spatial frequency composition of adjacent stimuli. Consequently, it would be predicted that, if the test and reference stimuli differ in their spatial frequency composition, depth discrimination thresholds should be asymmetric about the retinal disparity of the reference stimulus. We measured depth discrimination thresholds with test and reference stimuli that differed by up to 2 octaves in their spatial frequency composition. Stereo-thresholds decreased as a function of spatial frequency to about 2-4 c/deg and were then constant. However, in contrast to the predicted effects, our results show that, for the range of spatial frequencies used, differences of up to 2 octaves in spatial frequency, between test and reference stimuli, do not affect depth discrimination thresholds.

Depth Perception↗
PubMed1993

Precision of stereoscopic depth perception from double images.

The increment depth discrimination function was originally described by Ogle [(1953) Journal of the Optical Society of America, 43, 906-913] as a single exponential function. In contrast, recent studies have suggested that a two-component function better describes increment depth discrimination. To determine the relative effects of stereoscopic and non-stereoscopic width cues on the form of the function, we measured increment depth discrimination under conditions where both stereoscopic and dichoptic width cues were available. We found that increment depth discrimination data were well described by two-segment functions if both stereoscopic and dichoptic width cues were available. However, when dichoptic width cues were eliminated, by randomizing the pedestal disparity (crossed or uncrossed disparity) between trials, the increment depth discrimination function was better described by a single exponential function. This result has important implications for models of stereoscopic depth processing because it shows that stereoscopic depth discrimination thresholds progressively increase as a function of distance from the horopter.

Depth Perception↗
PubMed1992

Prior binocular dissociation reduces monocular form deprivation amblyopia in monkeys.

The profound visual deficits associated with early monocular form deprivation (MD) are caused largely by competitive binocular interactions in the visual cortex. We tested the hypothesis that disrupting normal cortical binocularity prior to the onset of MD would reduce the degree of form deprivation amblyopia compared to that produced in animals that had normal binocular vision prior to MD. An optical strabismus was maintained in two rhesus monkeys between 30 and 90 d old, a rearing strategy that substantially reduces excitatory cortical binocular interactions. Subsequently, the lids of one eye were sutured closed for 9 mo. Comparison data were obtained from a series of form-deprived monkeys reared in a normal manner prior to the onset of MD. Psychophysical procedures were employed to measure the effects of the rearing procedures on the spatial contrast sensitivity functions for each eye. By itself, MD resulted in a severe amblyopia. The spatial resolution of the deprived eyes of monkeys lid sutured by 5 mo of age was about 6 octaves lower than normal values (Snellen acuities of about 20/2000). In contrast, equivalent periods of MD had a much smaller effect on the spatial vision of the prism-reared monkeys. In both cases, the deprived-eye cut-off spatial frequencies were within 1 octave of the nondeprived-eye values and were comparable to cut-offs for binocularly form-deprived monkeys. The results demonstrate that prior binocular image dissociation protects young monkeys from the effects of MD, probably by reducing the potential for antagonistic, competitive binocular interactions in the visual cortex.

Amblyopia↗
PubMed1991

Binocular accommodative facility in prepresbyopic adults and its relation to symptoms.

Previous studies measuring accommodative facility have been confined to young adults and children. Standard test procedures were used to measure interactive facility (i.e., binocular accommodative flip test) in a sample of 45 adults from 30 to 42 years of age. The results showed a marked reduction in the average number of cycles per minute performed for the +/- 2.00 D flip test. Symptoms in the sample were also tabulated and their relation with interactive facility investigated. We found no direct relation between symptoms and accommodative facility. Further studies are needed to establish normative data for accommodative facility for adults approaching presbyopia.

Accommodation, Ocular↗
PubMed1990

The importance of the test parameters in the clinical assessment of accommodative facility.

Normative data for accommodative facility have recently become available. This study investigates the effect of varying the test parameters of lens power, target size, test distance, and test duration on binocular accommodative facility. Binocular accommodative facility decreased as a function of increasing lens power and decreasing target size. Differences in response times to the plus and minus phases of the flip test were not evident under any of the conditions. Interesting effects of proximity occurred at the nearer test distance. The results show the importance of strict control of testing procedures to achieve meaningful data.

Accommodation, Ocular↗