Speech paired sensory feedbacks enhancing the perception of embodiment of the reflection of face

Abstract

Embodiment is recognized as a paramount determinant of efficiency of mirror therapy (MT) and virtual reality (VR) techniques, which is generally induced by visual and proprioceptive feedback. However, emphasis on the embodiment of extremities hindered the combining of sensory feedbacks, like auditory feedback. The goal of this study is to investigate the effect of speech paired auditory and visuo-proprioceptive feedback on embodiment of the reflection of face during MT. Thirty-four participants were recruited and a customized camera-based MVF apparatus was employed to provide the mirror visual feedback (MVF). The experiment entailed three phases: rest (visual feedback), facial expression (viso-proprioceptive feedback) and enunciation (auditory and viso-proprioceptive feedback). Patients were required to imagine that the face in the screen was his/her own face during experiment. The embodiment was measured after each phase of the experiment using an 11-point Likert scale embodiment questionnaire, which was categorized as symmetry, ownership, agency, and deafference. The Friedman test revealed that the symmetry, ownership, and agency were related to the sensory feedbacks ( P < 0.001). The followed pairwise comparison demonstrated that embodiment was enhanced with the combining of sensory feedbacks; moreover, participants agreed more strongly with statements associated with symmetry, ownership, and agency when enunciating, comparing with rest or facial expression motions (all P < 0.05) (see Fig. 1). Sensory feedbacks play a crucial role of embodiment which might derive from the visual feedback. However, the combining of speech paired auditory and viso-proprioceptive feedback could significantly enhance embodiment, comparing with mere watching reflection or performing synchronised motions.