Lateral occipital (LO) cortex is a key node for object perception, but its contribution to attentional processing is largely unknown. Therefore we explored its role in a visual selective attention task with nonsense shapes by means of repetitive transcranial magnetic stimulation (rTMS).

Twenty-four healthy participants performed a task where, on the basis of a green/red cue, they were to make a same/different judgment between one of two overlapping nonsense shapes (the target, presented in the cued color), shown on the right of fixation, and a black comparison shape, shown on the left. After training, 5 rTMS blocks were alternated with 5 SHAM rTMS blocks. Five pulses of rTMS (10 Hz, 90% of the resting motor threshold) were delivered over left LO (localized by SofTaxic Optic 2.0), starting 50 ms before stimulus onset.

In addition to an overall facilitatory effect, rTMS shortened reaction times especially in a condition where the distracter (the item in the non-cued color), but not the target, matched the comparison shape, requiring more effective suppression to counteract conflict. Moreover, rTMS exerted this beneficial effect mainly in trials leading to long reaction times.

Our findings show that 1) LO is engaged to process nonsense shapes; 2) LO crucially contributes to the attentional selection of a relevant target in the face of potential distraction; and, finally, 3) rTMS can be used to modulate the efficiency of filtering mechanisms instantiated within LO cortex.