Decoding the motion aftereffect in human visual cortex

- Motion aftereffect direction can be decoded using fMRI pattern classification.
- Real and illusory motions in the same direction are differently encoded in the brain.
- MAE motion is neuronally most similar to real motion in orthogonal directions.
- Area MT has a unique role in generating the motion aftereffect.

In the motion aftereffect (MAE), adapting to a moving stimulus causes a subsequently presented stationary stimulus to appear to move in the opposite direction. Recently, the neural basis of the motion aftereffect has received considerable interest, and a number of brain areas have been implicated in the generation of the illusory motion. Here, we use functional magnetic resonance imaging in combination with multivariate pattern classification to directly compare the neural activity evoked during the observation of both real and illusory motions. We show that the perceived illusory motion is not encoded in the same way as real motion in the same direction. Instead, suppression of the adapted direction of motion results in a shift of the population response of motion sensitive neurons in area MT +, resulting in activation patterns that are in fact more similar to real motion in orthogonal, rather than opposite directions. Although robust motion selectivity was observed in visual areas V1, V2, V3, and V4, this MAE-specific modulation of the population response was only observed in area MT +. Implications for our understanding of the motion aftereffect, and models of motion perception in general, are discussed.