Attention influence response of Ebbinghaus illusion in the human visual area

Early visual areas encode visual information in retinotopic coordinates, signaling retinotopic size and orientation properties. One of the most fundamental properties of human primary visual cortex (V1) is its retinotopic organization, which makes it an ideal candidate for encoding spatial properties, such as size, of objects. However, Ebbinghaus contextual information can lead to size illusions that are reflected in the spatial pattern of activity in V1, V2 and V3. Here we used fMRI to measure BOLD response to a variant of the Ebbinghaus illusion to test where visual information processing starts to encode relative, opposed to retinotopic, sizes. Our result is consistent with the notion drat the Ebbinghaus illusion results from attention influence. This effect was significantly reduced when the focus of spatial attention was narrowed with a demanding fixation and central attention task. We reason that focusing attention on the fixation task resulted in reduced activity in. and therefore reduced feedback from higher visual areas that process the Ebbinghaus illusion.