Abstract
Task-irrelevant features are often present while a relevant task is being performed. Previous results showed that visual perceptual learning (VPL) occurs for such task-irrelevant features when they are perceptually weak (near detection threshold). Neuronal changes associated with such task-irrelevant VPL have remained largely unknown and are the focus of the current research. We employed a design in which participants (young adults, n=12) performed a rapid-serial-visual-presentation (RSVP) task at screen center while simultaneously being exposed to coherent motion in one direction as a task-irrelevant feature in the visual periphery. Participants performed the task over the course of twelve daily behavioral exposure sessions. Furthermore, they performed the task inside the scanner while brain activation was measured with functional MRI before the first, after the sixth and after the final behavioral exposure sessions. Participants were randomly assigned to one of two training groups, which differed only in the salience of the task-irrelevant feature (either near threshold for coherent motion detection or highly salient). As a result of the repeated exposure, participants in the threshold exposure group improved discrimination sensitivity for the exposed coherent motion direction, indicative of task-irrelevant VPL. These changes in sensitivity were associated with increased activation in early visual cortical areas representing the task-irrelevant coherent motion in the visual periphery. Trends for these results were already found after six behavioral exposure sessions but they became stronger pronounced after twelve behavioral exposure sessions, indicating that task-irrelevant VPL occurs slowly. A retest session three months after the final behavioral exposure session showed that task-irrelevant VPL and associated activation changes in early visual areas were partially long-lasting. No changes in sensitivity and activation in early visual areas were found with suprathreshold exposure, indicating that task-irrelevant VPL and activation changes in early visual areas occur primarily when the task-irrelevant feature is exposed near detection threshold.