Human perceptual learning in the peripheral visual field: sensory thresholds and neurophysiological correlates.

Perceptual learning in the peripheral visual field was studied in 24 adults using vernier targets. The aim was to relate perceptual improvements to changes of electrical brain activity. Thresholds were measured before, during, and after training, and on the next day. During training, the subjects passively looked at suprathreshold targets, and EEG activity was recorded from 30 electrodes over the occipital brain areas. Mean evoked potentials were computed for the first and second block of 1200 stimulus presentations, and the scalp topography of visual evoked potential (VEP) activity was analysed. Only for the stimulated area, training resulted initially in increased thresholds that, however, decreased significantly after consolidation. Electrical brain activity displayed smaller field strength and altered topography after training. Some of the effects were caused by habituation or adaptation to the training stimuli resulting in less efficient neurophysiological processing. The topographical changes indicate that different neuronal elements were activated after perceptual learning.