Figure 1.

Experimental design and stimuli. (A) Event-related adaptation design. Each trial began with a 4 s adapter stimulus (consisting of multiple different images of the same person randomly alternating every 0.2 s) followed by a blank screen for 0.5 s, followed by a 1 s probe stimulus. On SAME trials, the probe stimulus consisted of images of the same person as the adapter stimulus; on DIFF trials, the probe stimulus was of a different person. Each trial ended with a blank screen that lasted between 0.5 and 3.5 s. (B) Focused attention task (FOCUS condition). Subjects fixated a central cross while monitoring the face stimuli and were instructed to respond to infrequently occurring inverted faces by pressing a response button. The inverted face was shown for 100 ms and could appear at any time during either of the adapter or probe epochs. (C) Diverted attention task (DIVERT condition). Independent of and asynchronous with the face stimuli, subjects monitored a stream of letters at the center of the display and counted the number or target letters (X) among the distractors (Z, L, N, T). After 3 s, the letters were replaced by a cross, cueing subjects to indicate how many targets (between 0 and 3) they had seen.