Enhancing stereoacuity through perceptual learning in normal vision: Specificity for spatial frequency and orientation

Abstract

Purpose: To investigate whether practicing a stereoscopic depth detection task enhances stereoacuity in adults with normal vision and whether the learning effects, if any, transfer across target spatial frequencies and carrier orientations.

Methods: The visual stimulus consisted of two horizontally separated square blocks, one presented to each eye. Each block contained a Gabor target patch surrounded by four Gabor reference patches. A haploscope was used to enable binocular fusion. The visual task was to determine the stereoscopic depth of the Gabor target (in front / behind) relative to the four references. Ten adult observers with corrected-to-normal vision participated. The training protocol consisted of three training phases (each of 13 sessions). In Phase 1 observers were trained with targets with a vertical carrier of 5 cyc/deg (V5, vertical). In Phase 2 they continued to train with the same spatial frequency, but with an orthogonal carrier orientation (H5, horizontal). They were subsequently required to practice with targets with a vertical carrier at a higher spatial frequency (V10, 10 cyc/deg) in phase 3. Thresholds for each of the three stimulus configurations were measured before and after each training phase. Trial-by-trial feedback was provided.

Results: Our observers showed a substantial mean improvement of 64% in stereo thresholds after practicing with V5 stimuli in phase 1, and the improvement transferred substantially to the other two untrained stimulus configurations (H5: 46% and V10: 56%). Additional significant improvements obtained with subsequent direct-training in phases 2 (H5: 29%) and 3 (V10: 19%) indicate that the transfers observed in phase 1 were not complete.

Conclusions: Perceptual learning can induce functional plasticity for enhancing stereovision in the mature visual system. Our findings characterize the magnitude, time course and specificity of visual learning. This technique might have important applications in restoring impaired binocular vision in cortical visual disorders.

Keywords: 495 depth • 650 plasticity • 579 learning