Increasing EEG electrode density improves decoding of visual categories and source localization: an exploratory ultra-high-density EEG study

Understanding how the brain processes visual information is central to cognitive neuroscience. This exploratory study investigates the potential of ultra-high-density (uHD) electroencephalography (EEG) to capture neural dynamics during visual processing. We demonstrate that increasing EEG electrode density enhances spatial precision, improves the decoding of visual information, and facilitates more accurate source localization. Using a uHD EEG system with 512 electrodes focused over the occipital region, we recorded brain responses to four visual categories: faces, bodies, objects, and patterns. Our results show that higher electrode density facilitates more accurate single-trial classification of visual stimuli, achieving an average accuracy of 73% using uHD EEG and regularized linear discriminant analysis. Comparisons across different electrode layouts revealed that reducing electrode distance substantially affects decoding performance more than expanding the electrode coverage area. Additionally, higher electrode density resulted in more detailed topographic activation maps and improved source localization of the face-selective N170 component in the fusiform gyrus. While based on a limited number of participants, these findings highlight the critical role of electrode layout in visual EEG paradigms and demonstrate the promise of uHD EEG for high-resolution investigations across both research and clinical domains.