Abstract
Recently we reported that contrast and vernier learning transfers completely to a new location provided that the new location is primed by additional training with an irrelevant task/feature (Cur.Biol.2008), suggesting that learning may occur in non-retinotopic high brain areas. Here we demonstrate that perceptual learning also transfers across orientations in foveal vision with a similar double training paradigm.
Our results show that (1) Orientation discrimination learning for a foveal Gabor at ori_1 didn't transfer to orthogonal ori_2, replicating known orientation specificity. Neither did contrast discrimination learning at ori_2 transfer to orientation discrimination at the same ori_2. However, with simultaneous orientation training at ori_1 and contrast training at ori_2, orientation learning at ori_1 transferred to ori_2 completely; (2) Similarly, contrast learning at ori_1 didn't transfer to ori_2, and orientation learning at ori_2 didn't transfer to contrast discrimination at ori_2 either. But simultaneous double training resulted in complete transfer of contrast learning from ori_1 to ori_2; (3) Moreover, replacing contrast training in (1) with simple Gabor exposures at ori_2 for ∼2800 trials (subjects judged whether the stimulus was a Gabor (80% trials) or a letter C (20% trials)) also enabled nearly complete transfer of orientation learning from ori_1 to ori_2.
These orientation transfer results, along with our previous findings of complete location transfer of perceptual learning, invalidate location and orientation specificities as distinct characteristics of perceptual learning and question the inferred involvement of retinotopic early visual cortex. Rather they are more consistent with the Mollon-Danilova hypothesis that learning occurs at a central site. We propose that perceptual learning involves training-induced improvement of task-specific, but feature and location non-specific, decision-making in high brain areas. Learning transfers to a new location or orientation after additional training that improves spatial attention to the new location or feature attention to the new orientation.
Supported by Natural Science Foundation of China and US NEI