Experiment setup.

<p>Panel (a) shows normal and configurally-manipulated stimuli. Face stimuli of humans and macaques were placed on a gray background. Eyes and mouth were spatially displaced. Panel (b) shows the adaptation procedure for an upright macaque trial pair: the first trial (habituation) displays a macaque upright face in alternation with a blank, while the second trial (dishabituation) displays the same macaque upright face configurally manipulated in alternation with a blank. On- and offset of the stimuli are actively controlled by the observer's eye gaze. The ratio between picture and blank reflects the interest in the picture as a function of adaptation/habituation. The rebound of adaptation (dishabituation) reflects the relative rebound of interest in the second picture after having perceived the picture of the first trial. This indicates the perceive dissimilarity in two consecutive pictures.