The role of the angular gyrus in visual conjunction search investigated using signal detection analysis and transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) delivered over the posterior parietal cortex increases choice reaction times in visual search for a target defined by a conjunction of features. Some recent studies of visual search have taken an approach based on signal detection theory, the findings of which are not addressed by studying the disruptive effects of TMS on reaction time. Here we investigated the role of the posterior parietal cortex in visual search by applying TMS while subjects performed unspeeded feature and conjunction visual search tasks matched for level of difficulty. TMS over the right, but not the left angular gyrus (AG) in the parietal cortex, nor vertex decreased subjects' sensitivity on the conjunction but not the feature search task, as measured by the signal detection measure, d′. Changes in bias, specifically the tendency to make false positive responses, were less clear. We consider the findings in terms of four possible explanation: binding, attentional control, spatial localisation and visuomotor co-ordinate transformations.