Global motion adaptation

Image motion is initially detected locally. Local motion signals are then i ntegrated across space in order to specify the global motion of objects or surfaces. It is well known that prolonged exposure to motion causes adaptat ion at the local motion level. We have investigated whether adaptation also occurs at the global motion level. We have devised a global motion stimulu s (a random dot kinematogram) which has equal motion energy in opposite dir ections but nonetheless gives rise to global motion perception. At the loca l motion level, adaptation to this stimulus should cause equal adaptation i n both directions and should not give rise to an aftereffect. Any aftereffe ct seen must therefore be attributable to adaptation at the global motion l evel. We find that following adaptation to this stimulus, judgements of the perceived direction of a test pattern are systematically biased towards th e direction opposite to the adapting direction, suggesting that adaptation does occur at a level of visual processing at which global motion is repres ented. (C) 2000 Elsevier Science Ltd. All rights reserved.