Shifting attention between objects

Experiment I used a modified spatial cueing paradigm that was introduced by Egly et al. [J. Exp. Psychol. Gen. 123 (1994) 161] to investigate the cost incurred in shifting attention within an object as opposed to shifting att ention between objects. Subjects were presented with two outline rectangles and had to detect a target (a luminance increment) that could appear in th e cued location (valid trials), in an uncued Location inside the cued recta ngle (inside-invalid trials), or in an uncued location inside the uncued re ctangle (outside-invalid trials). Valid trials were faster than invalid tri als, and inside-invalid trials were faster than outside-invalid trials. In Experiment 2, the two rectangles were joined to form a unitary object. Hen, no difference was found between outside-invalid trials and inside-invalid trials. Experiment 3 showed that the delayed response on outside-invalid tr ials in Experiment 1 was not due to attention needing to cross the figural borders in order to re-orient to the uncued rectangle. The results were int erpreted as showing that an extra cost is incurred for shifting attention b etween different objects. (C) 2001 Elsevier Science B.V. All rights reserve d.