Face-contingent motion aftereffect

The demonstration of many types of contingent visual aftereffects suggests the existence of interactions between the two contingent properties somewhere in the visual processing stream. For example, the McCollough effect, or the orientation-contingent color after effect, implies that interaction between color and orientation. One view holds that contingent after effects are due to adaptation of neurons that are sensitive to the particular combination of the two visual features; another view maintains that contingent aftereffects are the result of associative learning. Although the exact neural mechanism of contingent visual after effects remains elusive, it is nevertheless informative to know what pairs of visual properties can induce contingent after effects. Here we examined whether motion after effect can be made contingent on human faces. Subjects (the two authors and two naïve observers) viewed alternating expanding faces and contracting scrambled faces for 5 minutes. After various amount of delay, static test images were presented to the observers. A weak, but reliable, face-contingent motion after effect was reported by both the authors as well as the two naïve observers. An static face was seen briefly moving in the opposite direction to the adapting face motion, whereas a static scrambled face was seen briefly moving in the opposite direction to the adapting scrambled face. Similar face-contingent motion after effect was seen with rotating motion. These contingent after effects were very weak immediately after the adaptation, but gained strength after minutes of delay, a signature of contingent visual after effects. This result suggests that, somehow and somewhere in the brain, motion of faces is represented differently than motion of non-faces.