Pupil Response as an Index for Perceived Tactile Stimulus Intensity

Abstract

The pupil response scales with stimulus intensity, observed in both visual and auditory modalities. It is unknown whether this generalizes to the tactile modality. Here, I investigated in healthy participants the relationship between pupil response and tactile stimulation applied to differently sensitive parts of the body and tactile stimulation of different intensity. In Experiment 1, pupil response was examined after tactile stimulation of the finger, arm, and calf. Participants (N=32) showed larger pupil response after stimulation of the finger versus arm and calf, and after stimulation of the arm versus calf. Using vibrotactile stimulation, pupil response after tactile stimulation of differential intensities was examined in Experiment 2 (N=20). Pupil response was smaller for weak tactile stimulation compared to medium and strong stimulation. Taken together, the current study showed differential pupil response after tactile stimulation on different body locations and after vibrotactile stimulation of different intensities. Tactile stimulation on more sensitive body locations may thus be perceived as more intense, based on comparable pupil response differences between tactile stimulation on body locations with differential tactile sensitivity and tactile stimulation of differential intensity. The current results indicate that pupil responses convey perceived intensity of tactile stimuli. Pupil response may have the potential to be used as an objective index for tactile sensitivity which is not reliant on verbal response from patients.