This is a proposal to continue measuring and modeling human psychophysical data that deal with spatial vision and its dependence on the temporal and chromatic parameters of the stimulus. We normally control the effects of eye movements on these interactions by stabilizing the retinal image and providing any desired motion or other temporal variations at the distal stimulus. This method of fixation control will be used in all the proposed studies. By a similar technique, we have simulated realistic scotoma conditions in normal subjects, which would be of value in studying the effects of pathologies that are located in the visual field. Topics we propose to study include: (1) Effects of both local and global adaptation processes on the thresholds for stabilized images, particularly isoluminance chromatic gratings. (2) Threshold and suprathreshold effects of retinal inhomogeneity on spatial vision, using large-area, quasi-sinusoidal targets. Previous experimental and theoretical results will be extended to include effects of target shape, temporal frequency and ultimately, chromatic gratings. By measuring contrast thresholds for circular targets whose spatial frequency varies with eccentricity, we will obtain spatiotemporal threshold surfaces, both luminous and chromatic, that are corrected for spatial inhomogeneity effects over a large retinal area. Cortically homogeneous stimuli produced in this way will also be used to study cortical mechanisms of spatial vision, with standard experimental techniques. (3) Suprathreshold contrast response surfaces, both luminous and chromatic, measured by a contrast-matching technique, will be compared with the results predicted from the threshold surfaces by a very general, nonlinear model. These comparisons will be used to isolate nonlinear mechanisms that are confined to local regions of the spatiotemporal frequency domain.
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