Standardized EEG Protocol for Comparing Cortical Responses to Mechanical and Electrical Tactile Stimuli

The development of realistic tactile feedback in haptic interfaces is contingent on understanding the neural processing of electrical versus mechanical stimuli. A protocol is presented for directly comparing the two modalities using electroencephalography (EEG). The protocol details procedures to achieve precise EEG-stimulator synchronization, calibrate subject-specific electrical and mechanical stimuli, and implement both oddball and roving paradigms to compare early event-related potential (ERPs) and the mismatch negativity (MMN) component. The proof-of-concept protocol was validated on four healthy participants, each assigned to a distinct experimental condition: mechanical or electrical stimulation of the right index fingertip under roving or oddball paradigms, manipulating duration (100 ms vs. 145 ms). Additionally, a 5^th participant underwent a roving paradigm with alternating modalities with all stimuli at 100 ms. Under unimodal stimulation, the roving paradigm proved more sensitive than the oddball in detecting somatosensory ERPs for both modalities and a discernible MMN-like component for electrical stimulation. The cross-modal comparison using the roving paradigm similarly revealed a clear MMN-like component but only for the electrical stimulus. These results demonstrate that the current protocol is suitable for correlating neural activity with perception and for directly comparing the cortical processing of artificial and natural sensations. This framework is a necessary step toward developing electrical stimulation protocols that elicit cortical responses indistinguishable from mechanical touch.