The simultaneous spatial frequency shift: a dissociation between the detection and perception of gratings.

Previous studies have shown that adaptation to a sinusoidal grating raises the contrast threshold for detecting gratings of similar spatial frequency and causes a shift in the apparent frequency of gratings of neighboring spatial frequency. In the present study the threshold rise and frequency shift were studied under two conditions: after adapting to a grating (successive condition) and while the test grating was surrounded by an inducing grating (simultaneous condition). The frequency shift was quantitatively similar under both conditions. Furthermore, the simultaneous shift was found to have the same dependence on the inducing contrast and orientation as did the successive shift. A rise in the threshold of the test grating, however, was found only in the successive condition. This indicates that the threshold rise and frequency shift are dissociated. A one-stage neural model was examined to see whether the frequency s h i f t could be quantitatively predicted from the threshold rise. The predictions were poor. A two-stage model was thus proposed to account for the results.