Modulation of the motion aftereffect by selective attention

THE motion aftereffect is a much studied and well documented phenomenon. After viewing a moving visual pattern for a period of time, the same pattern appears to drift in the opposite direction when it is stopped1. Psychophysical experiments involving inter-ocular transfer2,3, dichoptic stimulation4, and motion aftereffects contingent upon other visual parameters such as colour5,6, orientation5 and texture7, imply that the motion aftereffect is generated at the level of the visual cortex. It has been hypothesized that cortical neurons specialized for the detection of motion along a particular direction become 'fatigued' during the adaptation period so that the resting equilibrium subsequently shifts in the opposite direction to that of the adapting stimulus, giving rise to the sensation of the aftereffect8–13. I have found that if observers are engaged in a separate discrimination task superimposed on a moving textured background, the subsequent motion aftereffect to the background is considerably reduced. It seems that motion aftereffects are susceptible to attentional mechanisms.