The orientation specificity of two visual after-effects.

1. Inspection of a high-contrast adapting grating produces two visual after-effects: (a) the contrast threshold is raised for test gratings of similar spatial frequency to that of the adapting pattern and (b) the apparent spatial frequency of test gratings shifts away from that of the adapting grating-higher frequencies seem higher and lower ones lower than they really are.2. Both after-effects are orientation-specific. A horizontal adapting grating influences neither the threshold nor the apparent spatial frequency of vertical test gratings.3. The magnitude of the two after-effects was measured with vertical test gratings as a function of (a) tilt of a high-contrast adapting grating and (b) contrast of a vertical adapting grating.4. At all frequencies of the test grating, the decline of both after-effects produced by an increase in tilt of approximately 6(3/4) degrees could be matched by a reduction in contrast by a factor of 2.5. We take this as evidence for a common neural origin for these two visual phenomena.