Effects of prolonged practice on duration of spiral aftereffect: an ideographic study

The effects of prolonged practice on the duration of the spiral aftereffect were investigated; 3,000 trials over 30 days with 5 levels of ambient illumination were randomly presented to a single subject. Scores gradually decreased until a plateau was reached during the last 13 days. A large decrement during the last 5 days was attributed to a decision process component. An early difference in performance at different illumination levels was largely eliminated by the last 5 days.