Mapping Embodied Affective Touch Strategies on a Humanoid Robot

TL;DR

This study explores how affective touch strategies vary across different body regions and conditions on a humanoid robot, revealing body-region dependence and the influence of embodiment constraints.

Contribution

It provides a comprehensive analysis of affective touch across the full humanoid body, highlighting the impact of body region and physical constraints on touch behavior.

Findings

Touch location and dynamics are influenced by body region and spatial constraints.

Participants preferred upper-body regions for social touch and showed emotion-specific selectivity.

Affective touch strategies do not transfer directly between free and constrained conditions.

Abstract

Affective touch in human-robot interaction is shaped not only by emotional intent, but also by robot embodiment, including touch location, physical constraints, and perceived agency or social role. Existing HRI studies typically focus on one or two isolated body parts, limiting understanding of how affective touch generalises across the full humanoid body. We present a study with 32 participants interacting with the iCub robot, which is equipped with full-body distributed tactile sensors. Participants expressed eight emotions under three conditions: free touch, arm-only touch, and torso-only touch. Results show that body region and spatial constraints jointly shaped both touch location and dynamics. In free touch, participants preferred socially accessible upper-body regions, while less frequently touched areas showed stronger emotion-specific selectivity. Emotion-related variation was more evident in motion features for arm-only touch and pressure features for torso-only touch. Touch strategies also did not transfer directly between free and constrained conditions, even within the same coarse body region. Participants reported increased closeness to the robot after interaction, with around 30 percent reporting a change in perceived social relationship. Together, these findings show that affective touch expression is strongly body-region dependent and shaped by embodiment constraints.