TASK-DIFFICULTY AND THE SPECIFICITY OF PERCEPTUAL-LEARNING

Practising simple visual tasks leads to a dramatic improvement in perf orming them. This learning is specific to the stimuli used for trainin g. We show here that the degree of specificity depends on the difficul ty of the training conditions. We find that the pattern of specificiti es maps onto the pattern of receptive held selectivities along the vis ual pathway. With easy conditions, learning generalizes across orienta tion and retinal position, matching the spatial generalization of high er visual areas. As task difficulty increases, learning becomes more s pecific with respect to both orientation and position, matching the fi ne spatial retinotopy exhibited by lower areas. Consequently, we enjoy the benefits of learning generalization when possible, and of fine gr ain but specific training when necessary. The dynamics of learning sho w a corresponding feature. Improvement begins with easy cases (when th e subject is allowed long processing times) and only subsequently proc eeds to harder cases. This learning cascade implies that easy conditio ns guide the learning of hard ones. Taken together, the specificity an d dynamics suggest that learning proceeds as a countercurrent along th e cortical hierarchy. Improvement begins at higher generalizing levels , which, in turn, direct harder-condition learning to the subdomain of their lower-level inputs. As predicted by this reverse hierarchy mode l, learning can be effective using only difficult trials, but on condi tion that learning onset has previously been enabled, A single prolong ed presentation suffices to initiate learning. We call this single-enc ounter enabling effect 'eureka'.