Fig. 1.

Change localization/mean discrimination dual-task experiment. a Example stimuli. Sets were displayed successively for 1,000 ms each, separated by a 500-ms interval. On each trial, observers had to indicate (1) which set had the happier average expression (two-interval forced choice, 50% guess rate) and (2) any one of the four items that changed between the two sets (indicated here by the black outlines, not seen by participants; 25% guess rate). b Results. Overall, mean discrimination performance (left bar) was well above chance. Performance on the change localization task indicated that observers could attend to approximately three faces in the time allotted (middle bar). However, even when observers did not correctly localize a change between the sets (change localization miss trials), they were still significantly above chance in the mean discrimination task (right, gray bar; p < .001). This indicates that observers were able to discriminate the average expression in the group of faces on the same trials in which they failed to localize any individual face that changed. The black dotted line indicates chance performance on mean discrimination when change localization fails. Error bars indicate 1 SEM. *Performance significantly above chance