The perceived spatial frequency shift: evidence for frequency-selective neurones in the human brain.

1. Prolonged observation of a high-contrast grating pattern causes an apparent shift in the spatial frequency of gratings subsequently viewed with the same retinal region. Gratings of higher and lower frequency than the adapting pattern seem, respectively, higher and lower than in fact they are.2. There is no significant after-effect at the adapting frequency itself nor at frequencies more than two octaves away.3. For very low adapting frequencies, the after-effect remains centred at about 3.0 c/deg and declines in strength as the adapting frequency is successively lowered.4. The magnitude of the after-effect increases with the contrast of the adapting grating and the length of time spent in adaptation. It takes several hours to recover completely from 30 min adaptation.5. The phenomenon is orientation-specific: a horizontal adapting grating has no effect on vertical test gratings. There is partial interocular transfer of the after-effect.6. These findings provide further evidence that the visual system of man, like those of the cat and the monkey, contains neurones selectively sensitive to the orientation and dimensions of retinal images, and that these adaptable cells are actually involved in the encoding and perception of the size of simple patterns.