Sleep and the McCollough effect.

Orientation-contingent chromatic ("McCollough") aftereffects (OCCAs) were induced under carefully standardised conditions, in subjects suffering from varying degrees of sleep deprivation. The initial OCCA strength was found to vary systematically with the prior sleep pattern of the subject. In subjects whose sleep normally lasted 7-8 hr, loss of 3 or 4 hr of the previous night's sleep could reduce initial strength by as much as 50%; no further reduction was observed with still shorter sleep durations. Keeping the eye in darkness while awake had in this respect no comparable effects to those of sleep, and sleeping in a lighted room made no difference. The results suggest that the McCollough Effect depends on a form of neural plasticity which requires a normal sleep cycle for its maintenance.