Abstract
The current investigation sought to ellucidate the nature of the visual shape information responsible for the categorical perception of face stimuli (Rossion, Schiltz, Robaye, Pirenne & Crommelinck, 2001). A series of 11 faces corresponding to a linear continuum of morphed faces whose extremities consisted of specific facial identities was produced using a linear algorithm morphing program. By using the Bubbles technique (Gosselin & Schyns, 2001), we partially masked the morphed faces with patterns of randomly located Gaussian bubbles. Five subjects performed three experimental tasks (Levine& Beale, 2000). Subjects first completed a pre-training discrimination task in which they indicated which of two simultaneously presented morphed faces looked more like one of the continuum endpoints. Next, subjects classified each face along the continuum as more similar to one of the endpoint faces. We then repeated the discrimination task. Subjects produced a discontinuity in the likelihood of classifying the intermediate faces as more similar to one of the end-point faces at a location situated near the midpoint of the morphed continuum. This warrants that the faces were classified in a categorical manner. Moreover, potent information revealed by summing the bubbles leading to correct and incorrect classification responses indicates similar non-linear changes in the use of local facial feature information as the faces vary across the morphed continuum. The results suggest that the categorical perception mechanism for face recognition relies, in large part, on the saliency of componential information (the eyes seem particularly important).