Effects of attention on perceptual learning of shapes in the human visual cortex

Abstract

Perceptual learning and attention have been shown to modulate visual processing in the human brain. This study used fMRI to investigate the effect of these processes in the representation of shapes in early (V1, V2, VP, V4) and higher visual areas known to be involved in shape processing (Lateral Occipital Complex-LOC). The stimuli consisted of closed contours rendered by aligned gabor elements and embedded in two different background types: a) random gabor elements that interfered with the detection and integration of the contour elements (distributed attention condition) or b) uniformly-oriented elements that facilitated these processes (focused attention condition). We measured behavioral and fMRI responses while observers performed a 2-AFC shape discrimination task in two different sessions, one before and one after three days of training. Observers were trained in the distributed attention condition and were tested in both attention conditions on novel and learned shapes. Prior to training, no differences were observed in the behavioral performance or the fMRI responses across early and higher visual areas for the novel vs. the training shapes. After training, the observers showed significantly higher accuracy in the discrimination task for learned vs. novel shapes in both the distributed and the focused attention conditions. fMRI responses across visual areas were significantly stronger for learned than novel stimuli in the distributed attention condition. Interestingly, fMRI responses in the posterior subregion of the LOC (LO), known to be involved in the representation of shape features, showed stronger responses for novel than learned stimuli in the focused attention condition. These results suggest that increased shape saliency due to focused attention may enhance the tuning of the feature representation for familiar shapes and facilitate the representation of novel shape features