T C Handy, V Green, R M Klein, and G R Mangun (2001). J Exp Psychol Hum Percept Perform, 27(2):303-17.
Visual spatial attention has been likened to a “spotlight” that selectively facilitates the perceptual processing of events at covertly attended locations. However, if participants have advance knowledge of the likely location of an impending target and the likely response it will require, facilitation in response performance does not occur for targets at the expected (or attended) location that require an unexpected response. Event-related potentials (ERPs) were recorded during a discrimination task in which the most likely target location and target response were simultaneously cued prior to target onset. The ERPs showed evidence of enhanced perceptual-level processing for all targets at attended locations. These results suggest that the lack of response facilitation for unexpected targets at attended locations is likely due to postperceptual processes that are activated by the inclusion of nonspatial stimulus expectancies, response expectancies, or both.