Authors:

CUSACK, R., MITCHELL, D.J. & DUNCAN, J.

Reference:

Year of publication:

2006

CBU number:

6298

Abstract:

The intraparietal sulcus (IPS) is recruited across a range of tasks where a more difficult condition is compared to an easier one, suggesting it is part of a network of fronto-parietal regions that respond to multiple demands (MD). However, there is some evidence that the IPS responds to the presence and number of objects in the visual field, even after controlling for difficulty. From a meta-analysis, we show that the region of the IPS recruited across MD tends to be anterior to that recruited during the processing of objects. We ran an FMRI experiment to investigate this, comparing a task known to activate the fronto-parietal network (attention switching) with an object-based stimulus manipulation, using transparent dot surfaces, that recruits the dorsal visual stream. Attention switching was found to lead to sustained activation in frontal cortex, but had little effect in visual cortex. Conversely, the difference in stimulus properties led to transitory activity in visual (including V3a, LOC, MT) but not frontal regions. In contrast to the selectivity in these regions, many parts of the IPS were strongly activated by both task and stimulus differences. However, the anterior portion showed greater activation in response to attention switching than to the stimulus difference, while the posterior portion showed the opposite pattern. The anterior portion corresponded to the MD region from the meta-analysis, while the posterior portion corresponded to that activated in object processing studies, supporting greater specialisation for MD and object processing in the anterior and posterior IPS, respectively.