Neural Correlates of Mid-Air Haptic Stimulation Intensity

This study investigates how variations in the intensity of spatiotemporally modulated ultrasonic mid-air haptic stimulation modulate the amplitude, latency, and phase synchronization of somatosensory evoked potentials (SEPs), as well as their effect on behavioral perception. Electroencephalography recordings were obtained while stimulating the index and the middle finger of the left hand across different intensity levels, and a two-interval forced choice (2IFC) behavioral task was conducted to assess perceptual discrimination. The data revealed two dominant SEP components, a negative peak around 275 ms (N275) and a positive peak around 450 ms (P450), both showing increased absolute amplitude with higher stimulation intensity. Wavelet phase synchronization analysis further demonstrated great phase-locking stability at higher intensities. These findings indicate that mid-air haptic intensity modulated both the amplitude and temporal coherence of cortical responses. The behavioral results of the 2IFC task were consistent with the neural data. Participants reliably discriminated between intensity levels that exhibited distinct SEP amplitudes, while their performance declined for intensities that exhibited similar SEP amplitudes. Together, these results suggest that SEPs provide an objective neural correlate of subjective tactile perception. The study confirms that mid-air haptic stimulation can elicit intensity-dependent cortical responses, highlighting its potential for therapeutic, diagnostic, and interactive applications (e.g., virtual and augmented reality) despite its nontraditional stimulation mechanism. To our knowledge this is the first systematic integration linking intensity-dependent cortical responses to behavioral discrimination performance in mid-air haptic stimulation.