Representing Egocentric Directions with Torso-Applied Vibrotactile Stimuli

This paper investigates egocentric directional perception of azimuth and elevation in response to torso-based vibrotactile stimuli for both stimulus identification and direction association under a common experimental framework. We conducted four perceptual experiments that examined the two tasks for azimuth and elevation, using real vibrations and illusory stimuli generated by the funneling illusion. The results demonstrated that adding illusory stimuli effectively conveyed directional information with fewer tactors than using only real stimuli. Azimuth perception revealed a lateral bias, whereas elevation perception exhibited a downward bias on the dorsal torso, particularly in the upper back. However, both azimuth and elevation cues were generally consistent across vertical and horizontal torso locations. Additionally, we estimated regression models for both egocentric angles and showed that perceived directions could be estimated from actual stimulus positions. Correlation analysis revealed a weak relationship between azimuth and elevation perceptual errors, suggesting that these dimensions are processed with near-independence. Across all findings, azimuth cues proved to be more effective than elevation cues in conveying directional information. This study provides a comprehensive understanding of egocentric directions and offers practical insights for the design of torso-based vibrotactile displays.