We investigated whether lateral masking in the near-periphery, due to inhibitory lateral interactions at an early level of central visual processing, could be weakened by perceptual learning and whether learning transferred to an untrained, higher-level lateral masking known as crowding. The trained task was contrast detection of a Gabor target presented in the near periphery (4°) in the presence of co-oriented and co-aligned high contrast Gabor flankers, which featured different target-to-flankers separations along the vertical axis that varied from 2λ to 8λ. We found both suppressive and facilitatory lateral interactions at target-to-flankers distances (2λ - 4λ and 8λ, respectively) that were larger than those found in the fovea. Training reduces suppression but does not increase facilitation. Most importantly, we found that learning reduces crowding and improves contrast sensitivity, but has no effect on visual acuity (VA). These results suggest a different pattern of connectivity in the periphery with respect to the fovea as well as a different modulation of this connectivity via perceptual learning that not only reduces low-level lateral masking but also reduces crowding. These results have important implications for the rehabilitation of low-vision patients who must use peripheral vision to perform tasks, such as reading and refined figure-ground segmentation, which normal sighted subjects perform in the fovea.

A hallmark of modern Perceptual Learning (PL) is the extent to which learning is specific to the trained stimuli. Such specificity to orientation, spatial location and even eye of training has been used as psychophysical evidence of the neural basis of learning. This argument that specificity of PL implies regionalization of brain plasticity implicitly assumes that examination of a singular locus of PL is an appropriate approach to understand learning. However, recent research shows that learning effects once thought to be specific depend on subtleties of the training paradigm and that within even a simple training procedure there are multiple aspects of the task and stimuli that are learned simultaneously. Here, we suggest that learning on any task involves a broad network of brain regions undergoing changes in representations, read-out weights, decision rules, attention and feedback processes as well as oculomotor changes. However, importantly, the distribution of learning across the neural system depends upon the details of the training procedure and the characterstics of the individual being trained. We propose that to advance our understanding of PL, the field must move towards understanding how distributed brain processes jointly contribute to behavioral learning effects.

2 AbstractPurpose: The study investigated whether perceptual learning (PL) of a task consisting in detecting a low contrast Gabor patch flanked above and below by high contrast Gabor patches presented monocularly in the preferred retinal locus (PRL) of patients with macular degeneration (MD), improved their residual visual functions. Method:We measured contrast detection thresholds using both a Yes/No task (three MD patients and three controls) and a temporal two-alternative forced-choice task (2AFC; four MD patients and three controls).Results: Both tasks produced a significant improvement in contrast sensitivity for the trained target.However, only in the case of the temporal-2AFC this improvement depended on the target-toflankers distance. Furthermore, in both tasks PL improved visual acuity but with the temporal-2AFC task we found a higher degree of generalization of the training to untrained stimuli and tasks.In fact, we found a reduction of the crowding effect and an improvement of the contrast sensitivity for untrained spatial frequencies.Although PL is more effective with a temporal-2AFC task, it is also present with a Yes/No task, suggesting that PL reflects sensory enhancement, rather than improvement in decision mechanisms.Most importantly, follow-up tests on MD patients showed that PL effects were retained between four and eight months, suggesting PL induced long-term neural plasticity in the visual cortex. Conclusion:The results show for the first time that PL with a collinear configuration has strong, non-invasive and long lasting rehabilitative potential to improve vision in the PRL of patients with central vision loss.3