Strikingly rapid neural basis of motion-induced position shifts revealed by high temporal-resolution EEG pattern classification.

Several visual illusions demonstrate that the neural processing of visual position can be affected by visual motion. Well-known examples are the flash-lag, flash-drag, and flash-jump effect. However, where and when in the visual processing hierarchy such interactions take place is unclear. Here, we used a variant of the flash-grab illusion (Vision Research 91 (2013), pp. 8-20) to shift the perceived positions of flashed stimuli, and applied multivariate pattern classification to individual 64-channel EEG trials to dissociate neural signals corresponding to veridical versus perceived position with high temporal resolution. We show illusory effects of motion on perceived position in three separate analyses: (1) A classifier can distinguish different perceived positions of a flashed object, even when the veridical positions are identical. (2) When the perceived positions of two objects presented in different locations become more similar, the classifier performs less well than when they become more different, even if the veridical positions remain unchanged. (3) Finally, a classifier can discriminate the perceived position of an object even when trained on objects presented in physically different positions. These effects are evident as early as 81ms post-stimulus, concurrent with the very first EEG signals indicating that any stimulus is present at all. This finding shows that the illusion must begin at an early level, probably as part of a predominantly feed-forward mechanism, leaving the influence of any recurrent processes to later stages in the development of the effect.