Decoupling Orientation Specificity from Perceptual Learning in Amblyopic Vision

Abstract

Perceptual learning (PL) improves visual functions in amblyopes, but this learning is often specific to the trained orientation, possibly implying neural plasticity in the amblyopic early visual cortex. However, orientation specificity in normal vision can be decoupled from PL with a training-plus-exposure (TPE) technique (Zhang et al., 2010 Journal of Neuroscience 30 12323–12328), suggesting PL occurs in higher brain areas. Here we used the TPE in adults with amblyopia to investigate whether PL reflects V1 plasticity or improved high-level decision making in the amblyopic brain. Our results demonstrate that: (1) PL of contrast discrimination in the fovea of amblyopic eyes (AEs) did not transfer to an orthogonal orientation. However, AEs were then exposed to the orthogonal orientation through irrelevant orientation discrimination training, which enabled contrast learning to transfer to the orthogonal orientation. (2) We found similar transfer in the AEs after the non-amblyopic eyes (NAEs) were exposed. (3) Orientation specificity in Vernier and orientation learning was also eliminated by exposure of the transfer orientation in AEs or NAEs through irrelevant orientation or contrast training. (4) Surprisingly, orientation specificity in NAE Vernier learning was eliminated after AEs were exposed to the orthogonal transfer orientation, indicating the AE can teach the NAE. TPE-enabled learning transfer across orientations suggests that PL in amblyopic vision may not reflect plasticity in the amblyopic early visual cortex. Rather it may result from improved readout of noisy stimulus inputs at the decision stage, which compensates for the functional deficits in the amblyopic visual system.