The Neural Basis Underlying Improved Visual Function Of Adult Cats Through Contrast Sensitivity Training At A High Spatial Frequency

Extensive training improves the performance on the trained feature, a phenomenon which is known as perceptual learning (PL). Moreover, the learning effects could transfer to other tasks in some cases. Of the particular interests is the report that the learning in contrast sensitivity at high spatial frequency (SF) is not confined to improvement of contrast sensitivity, but also increases the visual acuity. While this training paradigm is a potential effective way to improve adults’ spatial vision, little is known about the neural mechanism underlying the transferred improvement in visual acuity. To answer this question, we trained four adult cats using orientation identification task at high SF and explored the underlying neural mechanisms with both behavioral and electrophysiological methods.In psychophysical experiments, we found that training significantly improved the contrast sensitivity of the trained eye at trained SF and also, the performance in the visual acuity test. Training effects transferred to the untrained eye and the visual acuity of untrained eye increased after training. Specifically, the improvement of the visual acuity curve exhibited some degree of SF specificity and stronger impact on trained eye. Furthermore, by assessing the training improvement in contrast thresholds for stimuli with and without added spatial noise, we demonstrated that the improvements in perceptual perormane after training was resulted from improved neural efficiency rather than decreased neural internal noise.In physiological experiments, we compared the contrast sensitivity and SF tuning properties of neurons in primary visual cortex (area 17) between three trained and four control cats. The results showed that not the neuronal contrast sensitivity, but the neuronal SF tuning properties changed after training. Specifically, the neurons of primary visual cortex in trained cats exhibited higher optimal spatial frequency (OSF) and better signal noise ratio (SNR). Morover, consistent with behavioral improvement, the neural changes also showed some degree of SF and eye specificity. Besides, for the monocular neurons of the trained cats, there were no significant differences in SF properties between trained and untrained eyes, suggesting that the training-induced plasticity in area 17 did not occur before binocular combination.In the end, the psychophysical and physiological results were compared and a significant correlation between the neuronal changes in area 17 (both the neuronal increase of OSF and enhancement of SNR) and the improvement of visual acuity was found. It suggests that neurons of area 17 may mediate the improved neural efficiency through changed SF representation and increased SNR, which results in improvement of behavioral performance.These results could not only deepen and improve our understanding of PL, but also help us to perfect and design new training paradigm to further improve visual abilities.