Exploring Interference between Concurrent Skin Stretches

TL;DR

This study tackles interference in multi-channel skin-stretch feedback by comparing collocated versus non-collocated placements across five distraction levels with two rocker-based forearm modules in 30 participants. Perception was quantified via the just-noticeable difference (JND) and intuitiveness via NASA-TLX, analyzed with mixed-effects models. Results show that distributing skin-stretch channels across two limbs lowers the JND, indicating reduced interference, while workload perceptions remain similar across configurations and distraction levels. These findings inform design choices for multi-channel skin-stretch systems, suggesting limb-separated layouts or alternative modalities to mitigate interference while maintaining intuitive feedback.

Abstract

Proprioception is essential for coordinating human movements and enhancing the performance of assistive robotic devices. Skin stretch feedback, which closely aligns with natural proprioception mechanisms, presents a promising method for conveying proprioceptive information. To better understand the impact of interference on skin stretch perception, we conducted a user study with 30 participants that evaluated the effect of two simultaneous skin stretches on user perception. We observed that when participants experience simultaneous skin stretch stimuli, a masking effect occurs which deteriorates perception performance in the collocated skin stretch configurations. However, the perceived workload stays the same. These findings show that interference can affect the perception of skin stretch such that multi-channel skin stretch feedback designs should avoid locating modules in close proximity.

Figures (5)

• Figure 1: The experiment setup shown in the one-hand configuration A and the two-hand configuration B. The primary skin stretch module (red band) was attached to the participant's left forearm at 10 cm from the wrist and the secondary skin stretch module (blue band) was attached 15 cm from the wrist at the left forearm in the one-hand configuration and the right forearm in the two-hand configuration. To prevent visual and audio cues, forearms with skin stretch modules were placed underneath the opaque table and earplugs were worn. In the two-hand configuration participants voiced their responses.
• Figure 2: The skin stretch module shown in side view A and isometric view B. The thickness and diameter of the skin stretch rocker are $13\,mm$ and $40\,mm$ respectively. The black outer layer of the rocker represents the adhered silicone rubber padding.
• Figure 3: The experiment protocol. The main experiment protocol A consisted of two sessions (one-hand and two-hand), each with five blocks of varying secondary skin stretch intensity. At the end of each block, participants completed a questionnaire (Q) followed by a 5-minute rest (R). Each block (shown in B) contained seven different conditions, repeated ten times. In all conditions (shown in C), a comparison was made against a standard skin stretch. The order of blocks, conditions, and primary skin stretch was randomized.
• Figure 4: Example response data and fitted psychometric curve for JND calculation. The $25\%$$(DL_{l})$ and $75\%$$(DL_{u})$ points (denoted by stars) were used to compute the JND as in (\ref{['eq: JND']}).
• Figure 5: JND and NASA-TLX results plotted by configuration and distraction levels. The results are shown as a violin plot, where the shape represents the data distribution and the middle bars represents the mean. The yellow and the blue colors correspond to the one-hand and two-hand configuration and the shades depict the distraction levels within the same configuration.