Dissociating neural activity associated with the subjective phenomenology of monocular stereopsis: an EEG study

Abstract

Abstracts 1The subjective phenomenology associated with stereopsis, of solid tangible objects separated 2 by a palpable negative space, is conventionally thought to be a by-product of the derivation of 3 depth from binocular disparity. However, the same qualitative impression has been reported 4 in the absence of disparity, e.g., when viewing pictorial images monocularly through an 5 aperture. Here we aimed to explore if we could identify dissociable neural activity associated 6 with the qualitative impression of stereopsis, in the absence of the processing of binocular 7 disparities. We measured EEG activity while subjects viewed pictorial (non-stereoscopic) 8 images of 2D and 3D geometric forms under four different viewing conditions (Binocular, 9 Monocular, Binocular aperture, Monocular aperture). EEG activity was analysed by 10 oscillatory source localization (beamformer technique) to examine power change in occipital 11 and parietal regions across viewing and stimulus conditions in targeted frequency bands 12 (alpha: 8-13Hz & gamma: 60-90Hz). We observed expected event-related gamma 13 synchronization and alpha desynchronization in occipital cortex and predominant gamma 14 synchronization in parietal cortex across viewing and stimulus conditions. However, only the 15 viewing condition predicted to generate the strongest impression of stereopsis (monocular 16 aperture) revealed significantly elevated gamma synchronization within the parietal cortex for 17 the critical contrasts (3D vs. 2D form). These findings suggest dissociable neural processes 18 specific to the qualitative impression of stereopsis as distinguished from disparity processing. 19 20 Keywords 21 Stereopsis, Monocular aperture, EEG, qualitative impression, parietal cortex, gamma 22 synchronization 23 1 Ames, A., 1925.