title: Faces in the mist: illusory face and letter detection.
abstract: We report three behavioral experiments on the spatial characteristics evoking illusory face and letter detection. False detections made to pure noise images were analyzed using a modified reverse correlation method in which hundreds of observers rated a modest number of noise images (480) during a single session. This method was originally developed for brain imaging research, and has been used in a number of fMRI publications, but this is the first report of the behavioral classification images. In Experiment 1 illusory face detection occurred in response to scattered dark patches throughout the images, with a bias to the left visual field. This occurred despite the use of a fixation cross and expectations that faces would be centered. In contrast, illusory letter detection (Experiment 2) occurred in response to centrally positioned dark patches. Experiment 3 included an oval in all displays to spatially constrain illusory face detection. With the addition of this oval the classification image revealed an eyes/nose/mouth pattern. These results suggest that face detection is triggered by a minimal face-like pattern even when these features are not centered in visual focus.
authors.affiliation: Department of Psychology, University of California, San Diego, La Jolla, CA 92093-0109, USA; e-mail:  crieth@ucsd.edu.
authors.forename: Cory A
authors.initials: CA
authors.lastname: Rieth
authors.forename: Kang
authors.initials: K
authors.lastname: Lee
authors.forename: Jiangang
authors.initials: J
authors.lastname: Lui
authors.forename: Jie
authors.initials: J
authors.lastname: Tian
authors.forename: David E
authors.initials: DE
authors.lastname: Huber
keywords: face perception; false detection; letter perception; reverse correlation; top down; vision