Visual adaptation has long been investigated in order to gain insight into the processing mechanisms of the human visual system. Traditionally, visual aftereffects have been studied and reported for early stages of processing and for relatively simple stimulus characteristics such as luminance, contrast (Chen, Zhou, Gong, & Liang,
2005), color, or motion (Antal et al.,
2004). One of the most popular and extensively investigated examples is the motion aftereffect (MAE) whose first mention is ascribed to Aristotle (
Parva Naturalia). Here, the prolonged viewing of a downward-moving stimulus subsequently leads to the illusionary perception of an upward motion in a static image (Purkinje,
1820; see Anstis, Verstraten, & Mather,
1998, for a review). This phenomenon has been explained to result from a disequilibrium between motion detectors tuned to opposite directions—with neural fatigue (Barlow & Hill,
1963) and reciprocal inhibition processes (Culham et al.,
1999; Tootell et al.,
1995) being discussed as the underlying neural mechanisms. The observation of this MAE (as one example of a well-established visual aftereffect) therefore revealed detailed and non-invasive insight into the organization of the neural system processing vertical motion—with one subsystem detecting upward motion and a second subsystem detecting downward motion. While adaptation to simple stimulus attributes has been known for literally hundreds of years, a striking novel discovery within the last few years was that adaptation is also of central importance for the perception of very complex visual stimuli. Webster and MacLin (
1999) reported the so-called face distortion aftereffect (FDAE)—a figural aftereffect affecting the perception of face configurations. They found that adaptation to distorted (e.g., contracted) faces subsequently led to an altered perception of normal faces: Participants perceived normal test faces as distorted in the direction opposite to adaptation (e.g., expanded). Similar high-level adaptation processes with contrastive aftereffects have also been reported for other face-related processes such as the perception of identity (Leopold, O'Toole, Vetter, & Blanz,
2001), gender (Kovács et al.,
2006), viewpoint (Fang, Ijichi, & He,
2007), ethnicity, and emotional expression (Webster, Kaping, Mizokami, & Duhamel,
2004). As in the investigation of adaptation effects for simple stimulus characteristics, figural high-level adaptation experiments with face stimuli allow a valuable insight into the mechanisms and functional organization of face perception: Webster and MacLin (
1999), for example, reported the FDAE to be asymmetric, i.e., adaptation to distorted but not to undistorted (“normal”) faces showed a clear effect on the perception of subsequently presented test faces. This is in line with the theory of a so-called “face–space” (Valentine,
1991) which suggests face representations to be organized in a multi-dimensional space with an average face prototype as the center (see also Leopold et al.,
2001).