Adaptation modulates the electrophysiological substrates of perceived facial distortion: Support for opponent coding

In two experiments we determined the electrophysiological substrates of figural aftereffects in face adaptation using compressed and expanded faces. In Experiment 1, subjects viewed a series of compressed and expanded faces. Results demonstrated that distortion systematically modulated the peak amplitude of the P250 event-related potential (ERP) component. As the amount of perceived distortion in a face increased, the peak amplitude of the P250 component decreased, regardless of whether the physical distortion was compressive or expansive. This provided an ERP metric of the degree of perceived distortion. In Experiment 2, we examined the effects of adaptation on the P250 amplitude by introducing an adapting stimulus that affected the subject’s perception of the distorted test faces as measured through normality judgments. The set of test faces was held constant and the adapting stimulus was systematically varied across experimental days. Adapting to a compressed face made a less compressed test face appear more normal and an expanded test face more distorted as measured by normality ratings. We found that the adaptation conditions that increased the perceived distortion of the distorted test faces also decreased the amplitude of the P250. Likewise, adaptation conditions that decreased the perceived distortion of the distorted test faces also increased the amplitude of the P250. The results demonstrate that perceptual adaptation to compressed or expanded faces affected not only the behavioral normality judgments but also the electrophysiological correlates of face processing in the window of 190–260 ms after stimulus onset. Adaptation techniques can be used to isolate neurophysiologcal mechanisms that are responsible for representing a stimulus. hrough extended exposure, the adaptation procedure recalibrates he encoding mechanisms that respond in the presence of an adaptng stimulus, resulting in systematic distortions of the perceptions f related stimuli, known as aftereffects. Adaptation aftereffects an alter the perception of subsequent stimuli in multiple ways. or example, adaptation to a distorted image can make a similarly istorted image appear more undistorted, while adaptation to the ame distorted image can make an image distorted in an opposite Please cite this article in press as: Burkhardt, A., et al. Adaptation modula Support for opponent coding. Neuropsychologia (2010), doi:10.1016/j.neur irection appear more distorted. Aftereffects based on the percepion of an object’s shape are termed figural aftereffects (Gibson, 933; Köhler & Wallach, 1944). An illustrative example of these patterns can be found in studies f faces, where the use of adaptation procedures has proven useful ∗ Corresponding author. Tel.: +1 812 855 1554; fax: +1 812 855 4691. E-mail address: lblaha@indiana.edu (L.M. Blaha). 028-3932/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. oi:10.1016/j.neuropsychologia.2010.08.016 © 2010 Elsevier Ltd. All rights reserved. to explore both the mechanisms for encoding face information and the temporal organization of those mechanisms. For example, Webster and MacLin (1999) demonstrated that perceptual adaptation to a compressed or expanded face caused a test face to appear distorted in the direction opposite to the adapting face. They showed that if one were to adapt to an expanded face, a normal test face would appear more compressed and an expanded face would appear more normal. Webster and MacLin (1999) termed this pattern of findings the face figural aftereffect, because it was based on the distortion of spatial or figural information within the adapting and test faces. Similar results have been found for identity aftereffects (Leopold, O’Toole, Vetter, & Blanz, 2001) in which adaptation to a particular identity alters the perceived identities of other faces. Strong aftereffects also occur following adaptation to face sex, race, and emotion (Webster, Kaping, Mizokami, & tes the electrophysiological substrates of perceived facial distortion: opsychologia.2010.08.016 Duhamel, 2004). These face aftereffects conform to the idea of norm-based encoding, where stimuli are encoded as a deviation from their psychological norm (Rhodes, Jeffery, Watson, Clifford, & Nakayama, 2003; Rhodes & Leopold, 2009; Valentine, 1991; Valentine & Bruce, 1986). Adaptation results in a temporary shift