Characterization of the functional interhemispheric connectivity using EEG and a bistable visual illusion of movement

Abstract

Visual illusions involve the dissociation of physical properties in visual stimuli, leading to altered or bistable perceptions. The Motion Quartet (MQT) is a widely studied paradigm in the field of illusions, generating apparent motion in vertical or horizontal direction. However, little is known about how perceptual grouping of the stimulus’ elements (either across or parallel to the vertical midline) depends on low-level features such as oriented contours associated to its elements and the exact region of the visual field it is presented in. Therefore, in this study, we presented variations of the MQT stimulus at different visual field positions while exchanging the elements with grating Gabor patches. We recorded multi-channel (64) electroencephalography (EEG) of healthy individuals indicating the direction of motion with button press. In order to investigate the inter- and intra-hemispheric connectivity of the visual cortex during the different types of illusory motion, we registered recordings with the subjectively perceived direction of motion and employed graph theory from complex systems. Thirty-two volunteers participated in the study, undergoing pre-evaluation, screening, and EEG experiments while performing the MQT task. We evaluated behavioral responses, including the number of switches and the time spent perceiving vertical and horizontal apparent motions, as well as inter-hemispheric connectivity and network analysis using computational metrics. Our findings reveal that in the central visual field, participants spent significantly more time perceiving horizontal motion when the MQT stimulus was presented horizontally, whereas the opposite pattern was observed in the periphery. Visually evoked potentials recorded from parieto-occipital electrodes did not differ between horizontally and vertically perceived motions, but variations were observed across the visual field positions. However, inter-hemispheric coherence and power-spectrum density displayed distinct differences based on the time spent perceiving the MQT stimulus. Short periods were characterized by increased frontal connectivity, while long periods perceiving horizontal motion showed increased coherences in the posterior region. Power-spectrum density did not differ significantly during short periods. Additionally, regardless of the global and local conditions, network metrics such as the number of edges, centrality measures, clustering coefficient, characteristic path length, small-worldness, assortativity, and efficiency differed between horizontal and vertical apparent motions, independent of the time spent perceiving them. This study provides novel insights into the interplay between visual illusions, neural connectivity, and behavioral responses in healthy individuals. Our findings highlight the impact of the visual field region on the perception of motion illusions and demonstrate distinct patterns of inter-hemispheric connectivity and network properties associated with different types of apparent motions. These results contribute to our understanding of the visual cortex's functional organization and shed light on the neural mechanisms underlying visual perception. Further research in this area may uncover additional factors influencing the perception of visual illusions and provide a foundation for potential applications in clinical populations with visual impairments or neurological conditions.