A second major finding from this study is that patients with amblyopia showed no binocular advantage. In visually healthy participants, response times have been shown to be shorter when subjects viewed binocularly rather than monocularly, even when the task involved two-dimensional displays that did not require stereopsis.
33 It has been proposed that during binocular viewing, the inputs from both eyes contain correlated stimulus signals that summate during visual processing, whereas the noise signals in the stimulus from each eye are uncorrelated, effectively cancelling each other when combined. As a result, the signal-to-noise ratio in the stimulus signals increases during binocular viewing, which, in turn, leads to more accurate, precise, and faster responses.
55 This binocular advantage, however, was not evident in people with amblyopia, as indicated by the observation that saccade latency during binocular viewing was no better than that during fellow eye viewing, possibly because of a disruption of binocular organization and a loss of binocularity in neurons in the visual cortex in amblyopia in general
56 –58 and in anisometropic amblyopia specifically.
13,58 Note, however, that a recent study demonstrated that binocular summation of contrast sensitivity is normal in people with strabismic amblyopia when stimulus contrast is adjusted to equalize visibility of the gratings for both eyes,
59 suggesting that the binocular summation deficits seen in previous studies
4,13,60 –64 may result from interocular differences in contrast sensitivity between the eyes.