Dissociation of attention and intention in human posterior parietal cortex: an fMRI study

In natural environments, the orienting of attention to an object of interest occurs jointly with selecting it as a potential target for action. This coupling of perceptual selection and motor planning has led to 'the premotor theory of attention', which argues that attention and intention share the same neural mechanism. Here we used fMRI to test this hypothesis by examining neural activity in the temporal parietal junction (TPJ) and intraparietal sulcus (IPS) of the posterior parietal cortex (PPC) while subjects searched for a target among distractors with the presence of color singletons. Task-relevant salience of stimuli and the variability of response time were used to characterize the behavior of attention and intention components of the visuomotor transformation performed in these two cortical regions, respectively. We found that TPJ responses were significantly higher when the color singletons were distractors (vs. targets), suggesting that the TPJ was involved in attentional control of interference from task-irrelevant but salient stimuli. In contrast, signals in the IPS were closely related to the variability of response time, with a larger BOLD response associated with longer RTs, suggesting that the IPS plays a pivotal role in intention by translating encoded information into action through evidence accumulation. Our data help to specify the functional division of labor between the IPS and TPJ and to further dissociate process components in visual search.