Adaptation aftereffects to facial expressions suppressed from visual awareness.

The study of adaptation aftereffects has been used as a tool to investigate the neural events that give rise to face perception. Recent adaptation studies suggest that face processing does not occur outside of awareness since identity- and gender-specific face aftereffects cannot be induced when the adapting face is rendered perceptually invisible using interocular suppression. However there is substantial evidence suggesting that facial expression, unlike identity and gender, is an attribute of faces that may recruit processes that are engaged automatically and independent of observers' awareness and attention. Therefore we investigated whether adaptation aftereffects specific to facial expressions could arise under continuous flash suppression (CFS). Our results show that adaptation to facial expressions is virtually abolished, when faces are suppressed from awareness. Moreover, this loss in aftereffect strength cannot be attributed to contrast adaptation exclusively, since results show only modest changes in perceived contrast following face adaptation. When observers endogenously attend to the location of the suppressed adapting stimulus, expression-specific aftereffects are enhanced. Our findings suggest that neural activity specifying affective information of facial expressions is highly vulnerable to the disruptive effect of interocular suppression, but that allocation of attentional resources can partially counteract suppression's effect.