Beyond balance: The role of the Vestibular system in action recognition

Abstract

Background: Action recognition is a fundamental aspect of human interaction. This process is mediated by the activation of shared sensorimotor representations during action execution and observation. Although complex movements involving balance or head and trunk rotations require vestibular signals for effective execution, their role in the recognition of others' actions is still unknown.

Objective: To investigate the causal involvement of the vestibular system in the discrimination of actions performed by others and whether this is influenced by motor familiarity.

Methods: In a single-blind design involving 25 healthy participants, Galvanic Vestibular Stimulation (GVS) was administered during an Action Discrimination Task (ADT), in which videos of actions categorized as vestibular/non-vestibular and familiar/unfamiliar were presented. Following each video, participants were required to identify the climax of the previously viewed action between two image options, using a two-alternative forced choice paradigm. The ADT was performed in active and sham GVS conditions, with left or right anodal montages. Response Times (RTs), Accuracy, and subjective motor familiarity were recorded for each action category.

Results: In sham GVS condition, an overall familiarity effect was observed, where RTs for familiar actions were faster than RTs for unfamiliar ones, regardless of vestibular engagement (p < .001; η_p ² = .80). Conversely, under active GVS, a selective interference of the identification of vestibular familiar actions was observed compared to sham. Specifically, GVS prolonged RTs for recognizing familiar vestibular actions (p = .004, d = .59) while concurrently enhancing visual sensitivity (d') for the same actions (p = .03, r = .21).

Conclusion: These findings demonstrate the contribution of the vestibular system to action recognition. GVS disrupted the sensorimotor representation of vestibular actions and led to increased reliance on an alternative processing system focused on visual analysis of limb positions. This dissociation provides valuable insights for future investigations into the complex relationship between vestibular signals and cognitive processes involved in action identification, essential for developing innovative GVS interventions, particularly for individuals with sensorimotor or vestibular disorders.

Keywords: Action recognition; Galvanic Vestibular stimulation; Mirror processing; Motor familiarity; Vestibular system; Visual sensitivity.

Fig. 1

(A). Experimental setting and GVS montage (B) Timeline for each trial of the Action Discrimination Task; (C) Timeline of the experimental session.

Fig. 2

Performance in the Action Discrimination Task for the four action categories. Response times (RT); visual sensitivity (d’); subjective motor familiarity for non-vestibular (a, b, c) and vestibular (d, e, f) actions. Data are presented as mean and standard deviation (SD), ∗p < .05, ∗∗p < .01, ∗∗∗p ≤ .001.

Fig. 3

Spearman's correlation between individual d' during Sham-GVS and response times during active-GVS for familiar vestibular actions.