Independent coding of object motion and position revealed by distinct contingent aftereffects.

Despite several findings of perceptual asynchronies between object features, it remains unclear whether independent neuronal populations necessarily code these perceptually unbound properties. To examine this, we investigated the binding between an object's spatial frequency and its rotational motion using contingent motion aftereffects (MAE). Subjects adapted to an oscillating grating whose direction of rotation was paired with a high or low spatial frequency pattern. In separate adaptation conditions, we varied the moment when the spatial frequency change occurred relative to the direction reversal. After adapting to one stimulus, subjects made judgments of either the perceived MAE (rotational movement) or the position shift (instantaneous phase rotation) that accompanied the MAE. To null the spatial frequency-contingent MAE, motion reversals had to physically lag changes in spatial frequency during adaptation. To null the position shift that accompanied the MAE, however, no temporal lag between the attributes was required. This demonstrates that perceived motion and position can be perceptually misbound. Indeed, in certain conditions, subjects perceived the test pattern to drift in one direction while its position appeared shifted in the opposite direction. The dissociation between perceived motion and position of the same test pattern, following identical adaptation, demonstrates that distinguishable neural populations code for these object properties.