Position shifts of fMRI-based population receptive fields in human visual cortex induced by Ponzo illusion

Abstract

Ponzo illusion is a well-known perceptual phenomenon in which the perceived sizes of visual objects are altered by visual depth cues created by converging lines at the horizon. One possible neural mechanism of the Ponzo illusion is the receptive field position shifts of V1 neurons, as supported by a recent monkey electrophysiological study (Ni et al. in Curr Biol 24(14):1653-1658, 2014). Here, we used fMRI-based population receptive field (pRF) mapping technique in combination of psychophysics to investigate this idea. We found that, relative to the close apparent depth in a 3D scene, the far apparent depth in the scene caused the pRF positions of voxels in V1-V3 to shift toward the fovea, in line with subjects' percept of the Ponzo illusion. Moreover, the pRF position shift in V1 significantly correlated with the magnitude of the Ponzo illusion across individual subjects. Our findings thus provide evidence for the close association between the perceived object size and the pRF position shift in human visual areas, especially in V1, lending further support for the receptive field position shift explanation for the Ponzo illusion.

Steady-state visually evoked potentials reveal partial size constancy in early visual cortex

“…This indicates that their neuronal size constancy, relative to perception, was somewhere between 20/35 ¼ 60% and 20/20 ¼ 100%. More recently, He et al (2015) found relatively low, but comparable effects for perception (6.3%) and for V1 population receptive fields (6.8%). Ni et al (2014) also investigated the Ponzo illusion, but looked at a corresponding shift of receptive fields in area V1 of macaque monkeys.…”

“…In general, the Ponzo illusion leads to striking effects on size constancy, but the corrections observed are typically less than 100% (Murray et al, 2006;Ni et al, 2014;He et al, 2015). This may be partly due to the use of monocular as opposed to stereo cues to depth.…”

“…Our result is consistent with previous fMRI studies showing that V1 activity changes with perceived size, when retinal size remains identical. Previous studies investigated the neural basis of size constancy with illusory size induced by pictorial cues (Murray et al, 2006;Fang et al, 2008;Liu, Wu, Yang, Campos, Zhang, & Sun, 2009;Ni et al, 2014;He et al, 2015), size adaptation (Pooresmaeili, Arrighi, Biagi, & Morrone, 2013), and with afterimages projected at different distances (Sperandio et al, 2012). We displayed real stimuli, rather than afterimages, at different physical distances.…”

“…constancy. In studies using pictorial illusions to induce perceived size changes a relatively good agreement between perceptual and physiological effects was found (Murray et al, 2006;Fang et al, 2008;Ni, Murray, & Horwitz, 2014;He et al, 2015). However, typically the perceptual effects used were modest, up to 30% change in perceived size, and the perceptual and physiological data were difficult to compare.…”

“…We are capable of perceiving the ''true'' constant, physical size of an object despite massive changes in the size its image subtends on the retina when it is seen at different distances (e.g., Holway & Boring, 1941). The neural basis of size constancy is still relatively unclear, but there have been several studies suggesting that a relatively size invariant representation of the world might arise as early as in primary visual cortex (Murray, Boyaci, & Kersten, 2006;Fang, Boyaci, Kersten, & Murray, 2008;Sperandio, Chouinard, & Goodale, 2012;Ni, Murray, & Horwitz, 2014;He, Mo, Wang, & Fang, 2015). This would be remarkable because early cortical areas have generally been described as having a strictly retinotopic organization (e.g., Engel, Glover, & Wandell, 1997;Tootell, Hadjikhani, Mendola, Marrett, & Dale, 1998;Wandell, Dumoulin, & Brewer, 2007).…”