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Individuals with scotomas in the center of their visual fields usually read much more slowly than visually impaired individuals without central scotomas. This study determines the extent to which inefficient eye movements could account for this difference. Using a technique described previously [Rubin and Turano (1992) Vision Research, 32, 895-902] text was(More)
The aim of this study was to test the hypothesis that an extra-retinal signal combines with retinal velocity in a linear manner as described by existing models to determine perceived velocity. To do so, we utilized a method that allowed the determination of the relative contributions of the retinal-velocity and the extra-retinal signals for the perception(More)
We evaluated the hypothesis that smooth pursuit eye movements affect speed discrimination thresholds of distal stimuli because they alter the retinal image speed. Subjects judged speed differences of sine-wave gratings while they simultaneously pursued a superimposed moving bar. Speed discrimination thresholds were measured, under conditions of controlled(More)
Motion can be perceived when a moving pattern is defined by variations in luminance. Motion can also be perceived when a moving pattern is defined by variations in contrast. The central focus of the present study was the isolation and description of the mechanism that is responsible for the processing of the movement of contrast variations. We measured(More)
Visual motion processes were studied with luminance- and contrast-modulated gratings. A sine-wave luminance grating was displaced abruptly back and forth by 3/16 cycle. The display sequence is ambiguous in that each 3/16-cycle phase shift (short-path motion) could just as readily be seen as a 13/16-cycle shift (long-path motion) in the opposite direction.(More)
Laboratory-based models of oculomotor strategy that differ in the amount and type of top-down information were evaluated against a baseline case of random scanning for predicting the gaze patterns of subjects performing a real-world activity--walking to a target. Images of four subjects' eyes and field of view were simultaneously recorded as they performed(More)
Eye movements add a constant displacement to the visual scene, altering the retinal-image velocity. Therefore, in order to recover the real world motion, eye-movement effects must be compensated. If full compensation occurs, the perceived speed of a moving object should be the same regardless of whether the eye is stationary or moving. Using a pursue-fixate(More)
OBJECTIVE To determine the association between performance on selected tasks of everyday life and impairment in visual acuity and contrast sensitivity. METHODS Visual acuity and contrast sensitivity were obtained on a population-based sample of 2520 older African American and white subjects. Performance was assessed on mobility, daily activities with a(More)