Learning-induced neural plasticity in vision

Learning is a fundamental process in biological vision that enables the visual system to benefit from perceptual experience and, thereby, to cope with a dynamic environment in an adaptive and efficient manner. What is the neural principle underlying visual learning? How is the learning controlled? To answer these questions, three studies examined learning-dependent neural plasticity.; The first study tested psychophysically how observers acquire top-down knowledge of visual objects in a noisy environment. Training improved the detection of novel dot patterns embedded in random dot backgrounds, but learning did not completely transfer either to untrained locations or to untrained shapes. Such partial specificity persisted for a month after training. Interestingly, training on shapes in empty backgrounds did not help segmentation of the trained shapes in noisy backgrounds. These results suggest that perceptual training increases the involvement of early sensory neurons in the segmentation of trained shapes, and that successful segmentation requires perceptual skills beyond shape recognition alone.; The second study, using functional magnetic resonance imaging (fMRI), examined the conditions in which ignored background information induces neural plasticity. During the task, subjects focused on the face stimuli at fixation while ignoring the scene stimuli in the periphery. The results indicated that increasing the perceptual difficulty of a foveal face task attenuated processing of task-irrelevant scenes in the background, while increasing the object working memory demands of the same task did not. These dissociable effects of perceptual and working memory load clarify how task-irrelevant, unattended stimuli are encoded in category-selective areas in human ventral visual cortex.; Finally, the last study further examined how attention controls the neural encoding of repeated stimuli, specifically testing whether attention is important for initial encoding, for the expression of memory traces, or for both. During the task, subjects were instructed to attend to either scenes or faces in composite (overlapping) scene-face images. The results showed a significant fMRI signal change in the scene-selective visual cortex only when scenes were attended both during the initial presentation and during repetition. These findings suggest that attention actively governs neural plasticity both during encoding and subsequent expression of the learned information.