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Ce Mo, Dongjun He, Fang Fang; Position shifts of fMRI-based population receptive fields induced by the Ponzo illusion. Journal of Vision 2015;15(12):1390. doi: 10.1167/15.12.1390.
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© ARVO (1962-2015); The Authors (2016-present)
Murray, Fang and colleagues (2006, 2008) demonstrated that the Ponzo illusion was reflected in the spatial pattern of activity in primary visual cortex (V1). They presented two rings at close and far apparent depths in a 3D scene (Fang et al. 2008). When subjects fixated its center, the far ring appeared to be larger and occupy a more eccentric portion of the visual field, relative to the close ring. Using fMRI, they found that the spatial distribution of V1 activity induced by the far ring was also shifted toward a more eccentric representation of the visual field, whereas that induced by the close ring was shifted toward the foveal representation. However, the nature of the V1 activity shifts remains largely unknown. A possible explanation is the position shift of receptive field of V1 neurons. Here, we used the fMRI-based population receptive field (pRF) mapping technique to test this possibility. We used the same stimuli as those in Fang et al. (2008). The magnitude of the Ponzo illusion was measured with a method of constant stimuli. The far ring appeared to be 0.17 degrees larger than the close ring. In the pRF mapping experiment, flickering checkered rings with various sizes were presented in the 3D scene and their center coincided with that of either the far ring or the close ring. Subjects were required to detect occasional, brief pauses of flickering. We found that, relative to the close ring, the pRF positions of the voxels in V1 and V2 responding to the far ring were closer to fixation, consistent with the perceptual appearance of the far and close rings. Furthermore, the pRF position shift in V1 significantly correlated with the illusion magnitude across individual subjects. These findings make headways towards unraveling the neural mechanisms of the Ponzo illusion.
Meeting abstract presented at VSS 2015
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