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Jian Ding, Dennis Levi; Recovery of stereopsis in human adults with strabismus through perceptual learning. Journal of Vision 2010;10(7):1124. doi: https://doi.org/10.1167/10.7.1124.
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© ARVO (1962-2015); The Authors (2016-present)
Stereopsis, the process leading to the sensation of depth from retinal disparity, is compromised or absent in strabismus and/or amblypia. Here we provide the first evidence for the recovery of stereopsis in human adults through perceptual learning - the repetitive practice of a demanding visual task with a feedback. Three strabismic adult observers (23-28 year old) without stereopsis but with normal visual acuity participated in the training. Before stereo training, the three observers failed the Randot circle test (≤ 400 arcsec), and also failed to detect a large binocular disparity (≤ 1320 arcsec) in stereoscopic sinewave gratings. Training trials began with a dichoptic cross and a binocular surrounding frame. By decreasing the contrast of the dominant eye's frame until both frames were visible, and adjusting the vertical and horizontal positions of the two frames separately, observers were able to achieve binocular fusion and alignment. Once fusion was achieved, a pair of sinewave gratings, one above the other with identical contrast and spatial frequency, was presented to the two eyes stereoscopically. The lower grating was presented in the same plane as the surround (zero disparity), and the upper grating was presented with a binocular disparity. The observer's task was to judge the relative depth of the top grating (i.e., closer or farther than the bottom grating). Feedback was provided after each trial. Following the training (thousands of trials), all three observers recovered stereopsis, achieving 40-140 arcsec stereoacuity with the Randot circle test, and were able to detect disparities of 70-280 arcsec with stereoscopic sinewave gratings which were jittered in horizontal position to avoid monocular cues. However, even after recovery of local stereopsis, our observers were unable to detect depth in random dot stereograms. We conclude that perceptual learning may be a useful clinical tool for treating stereoblindness.
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