Human perceptual learning is classically thought to be highly specific to trained stimuli's retinal location. Together with evidence that specific learning effects can result in corresponding changes in early visual cortex, researchers have theorized that specificity implies regionalization of learning in the brain. However, other research suggests that specificity can arise from learning readout in decision areas or through top-down processes. Notably, recent research using a novel double-training paradigm reveals dramatic generalization of perceptual learning to untrained locations when multiple stimuli are trained. These data provoked significant controversy in the field and challenged extant models of perceptual learning. To resolve this controversy, we investigated mechanisms that account for retinotopic specificity in perceptual learning. We replicated findings of transfer after double training; however, we show that prolonged training at threshold, which leads to a greater number of difficult trials during training, preserves location specificity when double training occurred at the same location or sequentially at different locations. Likewise, we find that prolonged training at threshold determines the degree of transfer in single training of a peripheral orientation discrimination task. Together, these data show that retinotopic specificity depends highly upon particularities of the training procedure. We suggest that perceptual learning can arise from decision rules, attention learning, or representational changes, and small differences in the training approach can emphasize some of these over the others.
