Abstract
The Flashed Face Distortion Effect (FFDE) is an illusion where faces viewed in rapid succession in the periphery are perceived as strongly distorted or caricatured (Tangen, Murphy, Thompson, 2011). The mechanisms contributing to the FFDE are largely unknown but could arise at many levels, including adaptation at both peripheral and central sites. Here we investigated whether pre-cortical processes play a role. For example, the response to each current image could be warped by local light adaptation or by Troxler-like fading of the preceding faces. To test for this we manipulated how successive faces are presented to each eye within a trial, using a dichoptic display. The faces (from the Karolinska Directed Emotional Faces, cropped to remove external features) within a trial were presented to either the left or right eye (monocular condition), both eyes (binocular condition), switched between eyes (interocular condition), or either the left or right eye but alternated with a gray field of the same duration between each face (control condition). The faces subtended a width of 3.3 degree with the closest edge at 2.5 degree eccentricity. Nine participants completed the conditions in randomized order, and used a sliding scale (from undistorted to very distorted) to rate the averaged level of face distortion at the end of each trial. We found that FFDE remained similar for interocular presentation - with comparable estimated distortion levels for monocular, binocular, and interocular conditions that were significantly larger than the control condition. These results suggest that early peripheral processes like local retinal adaptation, at least to the immediately preceding face may not significantly contribute to the FFDE.