A spatial frequency dependent grating-induction effect.

An inducing field containing a vertical sinewave luminance grating which surrounds a test field of similar space-average luminance induces within the homogeneous test field the appearance of a second sinewave grating of equal spatial frequency, but of opposite phase. The perceived contrast of the induced grating in the test field, as measured by a cancellation technique, can reach 90% that of the actual luminance contrast of the inducing grating. The perceived contrast of the induced grating decreases with increases in the spatial frequency of the inducing grating, and with increases in the dimension of the test field parallel to the orientation of the inducing grating. Square wave inducing gratings produce weaker induction effects than sinewave inducing gratings of the same spatial frequency and contrast. Additional observations indicate that the neural locus of this induction effect is cortical, lying at or beyond the level of spatial frequency selective channels.