ERP and functional connectivity reveal hemispheric asymmetry in perceptual grouping

The human visual system can effortlessly group small components into entities to form an object, but the role of the hemispheres in this processing is still unknown. Understanding the hemispherical processing of perceptual grouping is crucial for unraveling the complexities of visual perception. We have attempted to examine the processing of perceptual grouping in both hemispheres of the human brain. The neural data was collected for 15 healthy subjects while they viewed displays featuring either ‘structure’ (line segments composed of dots) or ‘non-structure’ (random dots). ERPs were recorded and assessed in both frontal and occipital regions of the left and right hemispheres for structure and non-structure stimuli. Our results revealed higher activation for structure compared to non-structure in both brain hemispheres, with notably amplified activity observed in the right hemisphere. Moreover, a decrease in task-related alpha power and an increase in PLI functional connectivity were observed during the perceptual grouping of structures. A novel finding that the Granger causality exhibits a higher value for perceptual grouping when information flows from the right to the left hemisphere, in contrast to communication from left to right, is obtained. Thus, the right hemisphere demonstrated distinct dominance in activation amplitude, task-related alpha power, functional connectivity, and directional functional connectivity related to perceptual grouping. Furthermore, our findings suggest that perceptual grouping involves communication between the frontal and occipital brain regions. By elucidating the hemispherical mechanisms underlying perceptual grouping, this research not only advances our understanding of basic cognitive processes but also offers practical implications for fields such as neurorehabilitation and artificial intelligence.