The direction aftereffect is driven by adaptation of local motion detectors

Abstract

The processing of motion information by the visual system can be decomposed into two general stages; point-by-point local motion extraction, followed by global motion extraction through the pooling of the local motion signals. The direction aftereffect (DAE) is a well known phenomenon in which prior adaptation to a unidirectional moving pattern results in an exaggerated perceived direction difference between the adapted direction and a subsequently viewed stimulus moving in a different direction. The experiments in this paper sought to identify where the adaptation underlying the DAE occurs within the motion processing hierarchy. We found that the DAE exhibits interocular transfer, thus demonstrating that the underlying adapted neural mechanisms are binocularly driven and must, therefore, reside in the visual cortex. The remaining experiments measured the speed tuning of the DAE, and used the derived function to test a number of local and global models of the phenomenon. Our data provide compelling evidence that the DAE is driven by the adaptation of motion-sensitive neurons at the local-processing stage of motion encoding. This is in contrast to earlier research showing that direction repulsion, which can be viewed as a simultaneous presentation counterpart to the DAE, is a global motion process. This leads us to conclude that the DAE and direction repulsion reflect interactions between motion-sensitive neural mechanisms at different levels of the motion-processing hierarchy.

Whether dots moving in two directions appear coherent or transparent depends on directional biases induced by surrounding motion

“…As a consequence, the perceived direction of the central stimulus, which is physically moving in a direction close to that of the surrounding motion, is biased away from the direction of the surrounding motion. This idea is in line with previous studies of the effect of motion adaptation on the perceived direction of a moving test stimulus (direction aftereffect; Curran, Clifford, & Benton, 2006;Curran et al, 2009;Levinson & Sekuler, 1976;Wilson & Kim, 1994). In the "Same Surround" condition used in the present study, the direction that is "suppressed" is identical to the average between the central two motions.…”

The hierarchy of directional interactions in visual motion processing

“…However, Kohn and Movshon note that their data can also be modelled by weakening feed-forward input from V1 into a recurrent model of MT circuitry, which would be consistent with a local motion-processing account of the DAE. Recent psychophysical data pointing to the DAE being a local motion phenomenon (Curran et al 2006a) support the latter interpretation.…”

Eye gaze direction shows a positive serial dependency

“…While there may be less benefit of a positive serial dependency for head position compared to eye position given the relative timescales of change typical for these stimuli, a negative (repulsive) serial dependency is thought to improve sensitivity to change. This follows as a consequence of repulsion from the recent stimulus increasing the apparent magnitude of change, as in the tilt and direction-of-motion aftereffects (Clifford, Wyatt, Arnold, Smith, & Wenderoth, 2001;Curran, Clifford, & Benton, 2006), which should increase discrimination performance provided noise variability does not increase by the same factor (Clifford et al, 2001). Given that head movements may be a more stable signal than eye movements, a negative dependency would be a useful way to improve perception of changes in head orientation.…”