The perceived spatial frequency, contrast, and orientation of illusory gratings.

Illusory vertical gratings (V) and diagonal gratings (D) can be seen on a uniform field after inspection of a vertical grating. When using simultaneous and successive matching techniques the spatial frequencies of the V effect were found to be about 2 octaves below and 1-2 octaves above the adapting spatial frequency, but to be invariant with temporal frequency. At high adapting frequencies the D effect dominated, and was about 0.8 octave below the adapting spatial frequency, oriented about +/-35 degrees from vertical. The apparent contrast of V was about twice the value of the contrast threshold at its apparent spatial frequency. D effects seen during adaptation were about 60 degrees from vertical and 3 octaves below the adapting frequency. The results are interpreted in terms of inhibition and disinhibition in an organized matrix of tuned channels, and the dominant pattern of inhibition in the matrix is inferred. Supporting evidence from neurophysiology, neuroanatomy, and psychophysics is briefly reviewed. An appendix deals with the question of interocular transfer of the aftereffect.