Task difficulty modulates electrophysiological correlates of perceptual learning.

To investigate the influence of task difficulty on the neural mechanisms of visual perceptual learning, we recorded event-related potentials (ERPs) from human adults while they were trained with either an easy or a difficult orientation discrimination task. The discrimination thresholds of participants trained with the difficult task decreased after training, but thresholds of participants with the easy task did not. More importantly, although posterior N1 reduction and anterior P2 decrement were obtained in both conditions, only the difficult task training showed an enhancement in posterior P1, an increase in N2 and P3, and a broader scalp distribution of posterior N1 attenuation. These differences indicated that the difficult task training affected the early visual processing stage, the later ERP components, and the broader visual cortical regions, respectively. The results in the present study provide direct electrophysiological evidence for task difficulty modulation of perceptual learning-related neuroplasticity.