title: Orientation processing mechanisms revealed by the plaid tilt illusion.
abstract: The tilt after-effect (TAE) and tilt illusion (TI) have revealed a great deal about the nature of orientation coding of 1-dimensional (1D) lines and gratings. Comparatively little research however has addressed the mechanisms responsible for encoding the orientation of 2-dimensional (2D) plaid stimuli. A multi-stage model of edge detection has recently been proposed [Georgeson, M. A. (1998) Image & Vision Computing, 16(6-7), 389-405] to account for the perceived structure of a plaid stimulus that incorporates extraction of the zero-crossings (ZCs) of the plaid. Data is presented showing that the ZCs of a plaid inducing stimulus can interact with vertical grating test stimulus to induce a standard tilt illusion. However, by considering the second-order structure of a plaid rather than ZCs, it was shown that the perceived orientation of the vertical test grating results from the combination of orientation illusions due to the first- and second-order components of an inducing plaid. The data suggest that the mechanisms encoding the orientation of second-order contours are similar to, and interact directly with, those that encode first-order contours.
authors.affiliation: Flight Management and Human Factors Division, NASA Ames Research Center, MS 262-2, Moffett Field, CA 94035-1000, USA. stuarts@vision.bhs.mq.edu.au
authors.forename: S
authors.initials: S
authors.lastname: Smith
authors.forename: P
authors.initials: P
authors.lastname: Wenderoth
authors.forename: R
authors.initials: R
authors.lastname: van der Zwan
mesh_terms: D015350:Contrast Sensitivity / Q000502:physiology; D006801:Humans; D015999:Multivariate Analysis; D009903:Optical Illusions / Q000502:physiology*; D009949:Orientation / Q000502:physiology*