Capturing 3D Skin Deformation and Finger Kinematics in Active Touch with Compliant Materials

In touch interactions with compliant materials, such as soft fruits and tissues, an individual's finger movements elicit unique and nuanced cutaneous and kinesthetic cues. The qualities of such cues are key to our perceptual judgments, but due to the spatiotemporal complexity of human touch, its contact interactions are difficult to capture and analyze. Prior efforts to quantify these cues have mostly been limited to passive touch, which constrains one's finger orientation, point of contact, forces, and displacements. Moreover, studies in active touch paradigms often only consider contact with rigid plates. This work describes a novel approach to measure cutaneous skin deformation and kinesthetic digit movements while exploring compliant materials in active touch. We use digital image correlation to track 3D skin surface deformation and quantify its compressive and tensile strain, cross-sectional curvature, and contact area. Additionally, optical sensors are used to track digit movements and quantify their joint angles, normal displacement, penetration depth, and applied force. We measure the effects of varying stimulus compliance (45 and 184 kPa elastomers) on active contact in human-subjects experiments and identify that participant-specific trajectories indeed generate differentiable changes across several skin deformation cues.