Sayoon Kim¹, Chai-Youn Kim¹; ¹Korea University

Pupillary response is known to vary parametrically with sensory intensity across modalities, reflecting automatic physiological tracking of stimulus magnitude (Wang & Munoz, 2015). While this relationship is well established in vision and audition (Binda & Murray, 2015; Zekveld et al., 2018), evidence in the tactile domain remains limited and inconsistent (Gusso et al., 2021). The present study examined how pupil dynamics change as a function of protrusion degree from a surface across visual, tactile, and visuo-tactile modalities. Stimuli were constructed as six degrees of protrusion, ranging from a flat surface (S0) to progressively increased intensity (S1–S5), presented as 3D-rendered images in the visual condition and 3D-printed objects in the tactile condition. Ten participants first completed a discrimination task to assess their ability to distinguish protrusion degrees in the visual and tactile modalities. Seven of these participants proceeded to the main experiment, in which they rated the perceived intensity of the stimuli in the visual, tactile, and visuo-tactile conditions while pupil diameter was continuously recorded with an eye tracker (Eyelink 1000, 1000Hz). Baseline-corrected pupil diameter was analyzed in two post-stimulus windows: an early window (500–1000ms) and a late window (1500–2000ms). A positive correlation between protrusion intensity and pupil dilation was significant in both time windows for the visual and visuo-tactile conditions, with the visual condition showing a particularly strong effect in the late window (r = 0.681, p < 0.0001). In the tactile condition, a positive correlation was found in the early window (r = 0.415, p = 0.0412) only when the flat surface (S0) was excluded. These findings indicate that pupillometry reflects the systematically varied intensity of the same physical surface property across visual, visuo-tactile, and, to some extent, tactile modalities.

Acknowledgements: Supported by NRF-2023R1A2C2007289