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Front. Neurosci. | doi: 10.3389/fnins.2019.00646

Identifying cortical substrates underlying the phenomenology of stereopsis and realness: A pilot fMRI study

 Makoto Uji1*, Angelika Lingnau2, Ian Cavin3 and  Dhanraj Vishwanath1
  • 1School of Psychology & Neuroscience, Faculty of Science, University of St Andrews, United Kingdom
  • 2Institute of Psychology, University of Regensburg, Germany
  • 3NHS Tayside, United Kingdom

Viewing a real scene or a stereoscopic image (e.g., 3D movies) with both eyes yields a vivid subjective impression of object solidity, tangibility, immersive negative space and sense of realness; something that is not experienced when viewing single pictures of 3D scenes normally with both eyes. This phenomenology, sometimes referred to as stereopsis, is conventionally ascribed to the derivation of depth from the differences in the two eye’s images (binocular disparity). Here we report on a pilot study designed to explore if dissociable neural activity associated with the phenomenology of realness can be localised in the cortex. In order to dissociate subjective impression from disparity processing, we capitalised on the finding that the impression of realness associated with stereoscopic viewing can also be generated when viewing a single picture of a 3D scene with one eye through an aperture. Under a blocked fMRI design, subjects viewed intact and scrambled images of natural 3-D objects and scenes under three viewing conditions: (1) single pictures viewed normally with both eyes (binocular) (2) single pictures viewed with one eye through an aperture (monocular-aperture); (3) stereoscopic anaglyph images of the same scenes viewed with both eyes (binocular stereopsis). Fixed-effects GLM contrasts aimed at isolating the phenomenology of stereopsis demonstrated a selective recruitment of similar posterior parietal regions for both monocular and binocular stereopsis conditions. Our findings provide preliminary evidence that the cortical processing underlying the subjective impression of realness may be dissociable and distinct from the derivation of depth from disparity.

Keywords: Realness, stereopsis, fMRI, parietal cortex, Intraparietal sulcus, 3d perception, Depth Perception

Received: 21 Feb 2019; Accepted: 05 Jun 2019.

Edited by:

Lars Muckli, University of Glasgow, United Kingdom

Reviewed by:

Raymond Van Ee, Radboud University Nijmegen, Netherlands
Paul B. Hibbard, University of Essex, United Kingdom  

Copyright: © 2019 Uji, Lingnau, Cavin and Vishwanath. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Makoto Uji, School of Psychology & Neuroscience, Faculty of Science, University of St Andrews, St Andrews, KY16 9JP, United Kingdom, mu6@st-andrews.ac.uk