Clues to the site of origin of the complementary image

Abstract

PATTERNS of near-parallel black-and-white lines induce an anomalous state of the visual system, in which a superimposed test field of dynamic noise (such as the ‘snowstorm’ on a detuned TV receiver) seems to stream in directions roughly perpendicular to the inducing contours¹. The illusory streamers form a ‘complementary image’ (CI) which for the stimulus of Fig. 1a comprises a family of wavy circles, as sketched by J. P. Wilson² in Fig. 1b. When two orthogonal gratings are superimposed, the streamers lie at 45° to both, as if the resulting bias obeys the rule of vector summation³. J. P. Wilson⁴ has observed rudimentary signs of directional bias and streaming even at a single black/white contour; and M. E. Wilson⁵, using only simple pairs of test spots illuminated in sequence, found that the illusory ‘phi’ motion seen between the spots was enhanced for directions orthogonal to the contours of a superimposed grating. When the inducing pattern is presented to one eye and the noise field to the other, however, little or no CI is observed^1,6. It has seemed logical¹ to attribute these phenomena to some form of adaptive cooperative activity among orientation-sensitive cells of the visual system, leading to a kind of ‘simultaneous contrast’ in the orientation domain, that is, a bias of the signalling system for motion and contour orientation in favour of the orientation(s) not present in the inducing stimulus.