Lateral occipital (LO) cortex is a key node for object perception, but so far its contribution to attentional processing is largely unknown. We therefore explored its role in a visual selective attention task with nonsense shapes using transcranial magnetic stimulation (TMS).

Subjects performed a task where, based on a green/red cue, they were to make a same/different judgment between one of two overlapping nonsense shapes (the one in the cued color) and a black comparison shape. Five pulses of TMS were delivered over left LO at 10Hz starting 450 ms before stimulus onset. TMS improved overall visual processing and selection of relevant shapes in all task conditions.

We next examined the effect of the same TMS protocol applied at a later time, starting 50 ms before stimulus onset, where we hypothesized more specific attentional effects. Interestingly, with this timing, TMS enhanced target processing especially in the most attention demanding condition when the distracter, but not the target, matched the comparison shape, requiring more effective distracter suppression in order to counteract conflict.

Overall, our results demonstrate that 1) LO is engaged to process nonsense shapes; 2) the specificity of perceptual and attentional consequences of LO TMS depends on stimulation timing; 3) LO crucially contributes to the attentional selection of a relevant target in the face of distraction; and, finally, 4) TMS can modulate the efficiency of filtering mechanisms within LO cortex.