Perceptual learning: psychophysical thresholds and electrical brain topography

We studied perceptual learning by determining psychophysical discrimination thresholds for visual hyper acuity targets (vernier stimuli) as a function of stimulus orientation. One aim was to relate perceptual improvements to changes of electrophysiological activity of the human brain. A group of 43 healthy adults participated in a psychophysical experiment where vernier th resholds for vertical and horizontal vernier targets were compared. In 16 s ubjects thresholds were measured for each orientation twice at an interval of 25 min. Between threshold estimations, evoked brain activity was recorde d from 30 electrodes over the occipital brain areas while the subjects obse rved appearance and disappearance of supra-threshold vernier offsets. Mean evoked potentials were computed for the first and second 600 stimulus prese ntations, and the scalp topography of electrical brain activity was analyze d. Vertically oriented stimuli yielded significantly better performance tha n horizontal targets, and thresholds were significantly lower in the second half of the experiment, i.e. after prolonged viewing of stimuli. The impro vements in discrimination performance were specific for stimulus orientatio n and did not generalize. Learning effects were also observed with electric al brain activity, and field strength of the potentials increased significa ntly as a function of time. Scalp topography of the evoked components was s ignificantly affected indicating a shift of activation between different ne uronal elements induced by perceptual learning. (C) 2001 Elsevier Science B .V. All rights reserved.