Binocular summation in orientation discrimination depends on stimulus
contrast and duration
Citation Info
Bearse M.A. Jr, and Freeman R. D. (1994)
Binocular summation in orientation discrimination depends on stimulus
contrast and duration.
Vision Res. 34: 19-29.
Abstract
Binocular summation, an improvement in visual performance with
binocular viewing compared to monocular viewing, has been studied
extensively in detection tasks. Monocular detection thresholds for
stationary stimuli are typically about 40% higher than binocular
thresholds. Binocular summation in discrimination tasks, however, is often
lower and less consistent. A possible explanation for this difference is
that saturation of responses limits the extent of binocular summation in
discrimination tasks. To investigate this possibility, we used an
orientation discrimination task and varied stimulus contrast and exposure
duration. Monocular and binocular orientation discrimination thresholds
were obtained using one-dimensional difference-of-Gaussian stimuli. For
briefly exposed stimuli, binocular summation is greatest at low contrasts
(e.g. 66% at 8% contrast) and is reduced systematically at higher contrasts
so that monocular and binocular thresholds are approximately equal at
contrasts above 15%. Binocular summation for low-contrast stimuli is
greatest at a brief exposure duration (50 msec), is reduced at longer
durations, and is not significant at durations of 100 msec or longer. Thus,
binocular summation in orientation discrimination is greatest for
relatively low-energy stimuli. These results are consistent with models of
binocular energy summation and the hypothesis that saturation of responses
after binocular combination can limit binocular summation in discrimination
tasks.
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