TMS Effect on Visual Search Task

Abstract

In this study, we examined the temporal aspects of the right posterior parietal cortex in easy feature and hard feature pop-out visual searches using transcranial magnetic stimulation (TMS). The transcranial magnetic stimulations were applied over the right posterior parietal cortex of subjects. Subjects received 4 tests which the TMS onset times were set as 100, 150, 200 and 250msec after visual stimulus presentation. We found that, when SOA=150msec, compared to no-TMS condition, There was a significant elevation in response time when the TMS pluses were applied. However for the other SOA cases, there was no significant difference between TMS and no-TMS conditions. Therefore, we considered that pop-out visual search was processed in the right posterior parietal cortex at about 150msec after stimulus present. visual stimuli for trials when the target was present. However, in the above-mentioned past researches, the temporal aspect of the right posterior parietal cortex (hereinafter abbreviated as PPC) in visual search was not discussed. In Ellison et al.'s rTMS study (8), they found that, TMS over the right PPC caused a significant increase in response time in the easy feature search and hard feature search. However, in their study, since the rTMS was applied before the visual search stimuli present, the involvement of the PPC in the visual search was confirmed but the time course was not addressed. In this study, to investigate the temporal aspect of the PPC involved in the pop-out visual search, we used different TMS stimulus onset asynchronies (SOA) and measured the visual search response times. The relationship between the SOA and the response time was investigated.