Pushing to and pulling away from salience: Evidence from rTMS for opposite biases in selection for the left and right posterior parietal cortex

Abstract

When the visual scene contains both the target of the current behavioural goal and competing distractors, visual attention must be engaged to resolve the emerging conflict by focusing on the target and suppressing the distractors. Here we examined the neural structures involved in these selective processes by applying offline repetitive Transcranial Magnetic Stimulation (rTMS) over right and left posterior parietal cortex (PPC) immediately before participants were asked to perform a Global-Local task using compound letters. The saliency of the information available at each level of the stimulus was varied orthogonally with whether local or global information had to be selected for the task. There was a double dissociation between the effects of rTMS to right and left PPC. When the more salient aspect of the stimulus had to be ignored, rTMS over the left PPC had a detrimental effect on performance. Conversely, rTMS over the right PPC made it more difficult to select the more salient aspect of the compound figure when it was relevant for the task. The data suggest critical roles for the left and right PPC in biasing attention away from and towards salient aspects of stimuli.