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7. Discrimination of time: comparison of foveal and peripheral sensitivity

Author

McKee, Suzanne P. and Taylor, Douglas G.

Abstract

Temporal processing is different in the periphery than in the fovea. Two measures of temporal sensitivity, increment thresholds for onset asynchrony and temporal modulation thresholds (flicker), were studied in the fovea and at 20 deg in the lower visual field. The ability to detect incremental changes in the time between the onsets of two vertical lines was generally more precise in the fovea than at the peripheral locus, at least for asynchronies ranging from 10 to 80 msec. Flicker thresholds were measured from 1 to 40 Hz with a vertical-line target used for the asynchrony thresholds. The peripheral flicker function peaks at a higher temporal frequency (15–20 Hz) than the foveal function (8–10 Hz); this suggests that the peripheral temporal impulse response follows a faster time course than the foveal impulse response. Asynchrony discrimination would potentially provide a simple estimate of the temporal sensitivity underlying velocity discrimination. We find that asynchrony discrimination is not a good predictor of velocity thresholds; it fails at the high velocities at which velocity discrimination is most precise.

Published
1984

8. The precision of binocular and monocular depth judgments in natural settings.

Author

McKee SP and Taylor DG

Subjects
Humans, Depth Perception physiology, Sensory Thresholds physiology, Vision, Binocular physiology, Vision, Monocular physiology
Abstract

We measured binocular and monocular depth thresholds for objects presented in a real environment. Observers judged the depth separating a pair of metal rods presented either in relative isolation, or surrounded by other objects, including a textured surface. In the isolated setting, binocular thresholds were greatly superior to the monocular thresholds by as much as a factor of 18. The presence of adjacent objects and textures improved the monocular thresholds somewhat, but the superiority of binocular viewing remained substantial (roughly a factor of 10). To determine whether motion parallax would improve monocular sensitivity for the textured setting, we asked observers to move their heads laterally, so that the viewing eye was displaced by 8-10 cm; this motion produced little improvement in the monocular thresholds. We also compared disparity thresholds measured with the real rods to thresholds measured with virtual images in a standard mirror stereoscope. Surprisingly, for the two naive observers, the stereoscope thresholds were far worse than the thresholds for the real rods-a finding that indicates that stereoscope measurements for unpracticed observers should be treated with caution. With practice, the stereoscope thresholds for one observer improved to almost the precision of the thresholds for the real rods.

Published
2010
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