Continuous sliding pressure feedback enhances supernumerary robotic thumb proprioception over discrete vibrotactile feedback: behavioral and EEG evidence.

Abstract

Objective. Supernumerary robotic thumbs (SRTs) offer promising augmentation capabilities, yet their adoption remains limited by the lack of reliable proprioceptive awareness, which is critical for enabling intuitive control and cognitive integration. Vibrotactile (VF) and pressure feedback (PF) represent two widely used modalities for proprioception that differ fundamentally in their encoding of information: VF feedback is widely adopted due to its low cost and ease of wearability, but provides discrete, temporally patterned cues, whereas PF is expensive and bulky yet it delivers continuous, analog signals that more closely resemble natural proprioceptive input.Approach. This study compares discrete VF and continuous sliding PF for conveying SRT proprioceptive information in the absence of visual input, combining behavioral assessment with electroencephalography. A total of 42 participants were recruited and assigned to either a VF or PF group; they wore the SRT, received modality-specific sensory feedback during passive finger movements, and were asked to decode the start and end location of the finger's motion. Sensorimotor event-related desynchronization (ERD) in the alpha and beta bands and beta-band functional connectivity were analyzed to characterize cortical differences between modalities.Main results. Both modalities outperformed implicit feedback, with PF demonstrating superior accuracy compared to VF. VF elicited more sustained alpha-band ERD across both contralateral and ipsilateral sensorimotor cortices and sustained beta-band ERD in the ipsilateral sensorimotor cortex, suggesting prolonged cortical engagement and increased processing demand. PF elicited significantly higher beta-band small-worldness, indicating more efficient network-level integration of proprioceptive information.Significance. These findings demonstrate that continuous, analog feedback more effectively conveys proprioceptive information and sensorimotor integration than discrete, temporally encoded cues; informing the design of sensory augmentation systems that effectively integrate artificial limbs into the human body schema.