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Thomas H Wu, Ashley Craven, Truyet Tran, Kenneth Tran, Kayee So, Dennis M Levi, Roger Winghong Li; Enhancing coarse-to-fine stereo vision by perceptual learning: An asymmetric transfer across spatial frequency spectrum. Invest. Ophthalmol. Vis. Sci. 2014;55(13):751.
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To investigate whether perceptual learning improves coarse and fine stereopsis and to examine the bandwidth of transfer of learning, if any, across spatial frequency.
The visual stimulus consisted of two horizontally separated square blocks, one presented to each eye. Each block contained a Gabor target patch (with a vertical carrier) surrounded by four Gabor reference patches. A haploscope was used to enable binocular fusion. Binocular disparity was introduced by shifting the two Gabor targets in opposite directions. The visual task was to determine the stereoscopic depth of the Gabor target (crossed disparity: in front of / uncrossed disparity: behind) relative to the four references. Twenty adult observers with normal vision were randomly assigned to two groups (LH and HL). In phase 1, group LH was trained at a low spatial frequency (1.25 cpd) and group HL was trained at a high spatial frequency (20 cpd). In phase 2 observers “crossed over” and trained at the untrained spatial frequency (group LH: 20 cpd; group HL: 1.25 cpd). To determine the bandwidth of transfer across the spatial frequency spectrum, thresholds were measured at each of four spatial frequencies (1.25, 5, 10 and 20 cpd) before and after each training phase. Observers were given more than 15000 trials over 31 sessions. Trial-by-trial feedback was provided.
Direct training resulted in substantial improvements in mean stereo thresholds (group LH: 70%; group HL: 78%). There was an asymmetric transfer of learning effect to the “untrained” spatial frequencies (group LH: 44%; group HL: 59%). Additional improvements obtained with subsequent direct-training in group LH (35%) and group HL (11%) indicate that the transfer was stronger from high to low spatial frequency than from low to high.
Perceptual learning can sharpen coarse-to-fine stereopsis. Our findings suggest that stereovision training is most beneficial across the spatial frequency spectrum when trained at a high spatial frequency. Our findings characterize the magnitude, time course and specificity of visual learning. This technique might have important applications in restoring impaired binocular vision in clinical situations.
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