Examining the dissociation of retinotopic and spatiotopic inhibition of return with event-related potentials.

Inhibition of return (IOR) is thought to reflect a mechanism that biases orienting which, under some circumstances, reduces perceptual processing at previously processed locations. Studies using event-related potentials (ERPs) have generally revealed that IOR is accompanied by an amplitude reduction of early sensory ERP components (e.g., P1). While behavioral studies suggest that IOR may be represented in both spatiotopic and retinotopic coordinates, all previous ERP studies have used the prototypical spatial cueing paradigm and have thus confounded retinotopic and spatiotopic reference frames. Because of this confound it is unknown whether the P1 reduction that has been associated with IOR will be observed in retinotopic or spatiotopic coordinates when these are dissociated. The current experiment investigated whether the P1 component would be modulated by IOR when the retinotopic and spatiotopic reference frames were dissociated by an eye movement between cue and target onset. Strong spatiotopic IOR was found to be accompanied by a negative difference (Nd) in the 200-300 ms time window, while a P1 reduction was absent, suggesting that P1 reductions do not provide an accurate reflection of IOR.