The direction after-effect is a global motion phenomenon.

William Curran,Lee Beattie,Jade A Currie,Delfina Bilello,Jessica M Pimentel Leon,Laura A Coulter

doi:10.1098/rsos.190114

Abstract

Prior experience influences visual perception. For example, extended viewing of a moving stimulus results in the misperception of a subsequent stimulus's motion direction—the direction after-effect (DAE). There has been an ongoing debate regarding the locus of the neural mechanisms underlying the DAE. We know the mechanisms are cortical, but there is uncertainty about where in the visual cortex they are located—at relatively early local motion processing stages, or at later global motion stages. We used a unikinetic plaid as an adapting stimulus, then measured the DAE experienced with a drifting random dot test stimulus. A unikinetic plaid comprises a static grating superimposed on a drifting grating of a different orientation. Observers cannot see the true motion direction of the moving component; instead they see pattern motion running parallel to the static component. The pattern motion of unikinetic plaids is encoded at the global processing level—specifically, in cortical areas MT and MST—and the local motion component is encoded earlier. We measured the direction after-effect as a function of the plaid's local and pattern motion directions. The DAE was induced by the plaid's pattern motion, but not by its component motion. This points to the neural mechanisms underlying the DAE being located at the global motion processing level, and no earlier than area MT.

Highlights

Motion encoding by the visual cortex is a hierarchical process, with local motion information extracted during the early stages of visual processing and global motion information extracted at the later stages [1,2,3,4]
We know from previous research that the neural mechanisms that drive the direction after-effect (DAE) are cortical [25,26], but to date there has been no consensus on where in the cortex these mechanisms are to be found—at the level of local motion processing or at the global motion processing level (MTþ)
To this end we used an adaptor, a unikinetic plaid, which we argue is ideal for separating the effects of local and global motion adaptation

Summary

Introduction

Motion encoding by the visual cortex is a hierarchical process, with local motion information extracted during the early stages of visual processing and global motion information extracted at the later stages [1,2,3,4]. Curran et al [25] investigated the cortical locus of the DAE by measuring its speed tuning function, and using a number of mixed-speed adaptors in an attempt to test DAE magnitude predictions made by local and global models Their results suggest the DAE is driven by adaptation of local motion processing mechanisms and the authors conclude that these results, along with their finding that the DAE undergoes incomplete DAE magnitude increased linearly with increasing adaptor motion coherence signal [34] Given that these results were predicted based on the known response characteristics of MT neurons in area MT, they support the position that the DAE is driven by adaptation at the global motion processing level. A DAE would be expected to occur in the latter case because the component motion direction is non-vertical

Methods

Apparatus and stimuli

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Results

Discussion