Inter-attribute tilt effects and orientation analysis in the visual brain

A test grating appears to be tilted away from an inducing grating for small angular separations (repulsion), but towards the inducing grating for larger angular separations (attraction). Previous research on luminance gratings suggests that repulsion is caused by local inhibition in cortical areas V1 and/or V2, and that the attraction involves global interactions beyond V1, in extrastriate areas. Experiments reported here demonstrate attribute invariant attraction and repulsion effects for gratings specified by luminance, motion, and disparity contrasts. A frame surrounding the inducing grating abolishes only the attraction effect, but a spatial frequency difference, or a small gap between the inducer and test gratings, abolishes only the repulsion effect, irrespective of the attributes that specify the gratings. It is proposed that detectors selectively sensitive to attribute invariant orientation and size exist in early cortical sites such as V1 and/or V2.