Effects of daily training amount on visual motion perceptual learning.

Perceptual learning has been widely used to study the plasticity of the visual system in adults. Owing to the belief that practice makes perfect, perceptual learning protocols usually require subjects to practice a task thousands of times over days, even weeks. However, we know very little about the relationship between training amount and behavioral improvement. Here, four groups of subjects underwent motion direction discrimination training over 8 days with 40, 120, 360, or 1080 trials per day. Surprisingly, different daily training amounts induced similar improvement across the four groups, and the similarity lasted for at least 2 weeks. Moreover, the group with 40 training trials per day showed more learning transfer from the trained direction to the untrained directions than the group with 1080 training trials per day immediately after training and 2 weeks later. These findings suggest that perceptual learning of motion direction discrimination is not always dependent on the daily training amount and less training leads to more transfer.

Cortical Reorganization of Peripheral Vision Induced by Simulated Central Vision Loss.

When one's central vision is deprived, a spared part of the peripheral retina acts as a pseudofovea for fixation. The neural mechanisms underlying this compensatory adjustment remain unclear. Here we report cortical reorganization induced by simulated central vision loss. Human subjects of both sexes learned to place the target at an eccentric retinal locus outside their blocked visual field for object tracking. Before and after training, we measured visual crowding-a bottleneck of object identification in peripheral vision, using psychophysics and fMRI. We found that training led to an axis-specific reduction of crowding. The change of the crowding effect was reflected in the change of BOLD signal, as a release of cortical suppression in multiple visual areas starting as early as V1. Our findings suggest that the adult visual system is capable of reshaping its oculomotor control and sensory coding to adapt to impoverished visual input.SIGNIFICANCE STATEMENT By simulating central vision loss in normally sighted adults, we found that oculomotor training not only induces PRL, but also facilitates form processing in peripheral vision. As subjects learned to place the target at an eccentric retinal locus, "visual crowding"-the detrimental effect of clutter on peripheral object identification-was reduced. The reduction of the crowding effect was accompanied by a release of response suppression in the visual cortex. These findings indicate that the adult visual system is capable of reshaping the peripheral vision to adapt to central vision loss.