Are expression aftereffects fully explained by tilt adaptation?

Facial expressions are used as critical social cues in everyday life. Adaptation to expressions causes expression aftereffects. These aftereffects are thought to reflect the operation of face-selective neural mechanisms, and are used by researchers to investigate the nature of those mechanisms. However, recent evidence suggests that expression aftereffects could be at least partially explained by the inheritance of lower-level tilt adaptation through the visual hierarchy. We investigated whether expression aftereffects could be entirely explained by tilt adaptation. Participants completed an expression adaptation task in which we controlled for the influence of tilt by changing the orientation of the adaptor relative to the test stimuli. Although tilt adaptation appeared to make some contribution to the expression aftereffect, robust expression aftereffects still remained after minimizing tilt inheritance, indicating that expression aftereffects cannot be fully explained by tilt adaptation. There was also significant reduction in the expression aftereffects after inverting the adapting face, providing evidence that face-selective processing is involved in these aftereffects.