Involvement of visual signals in kinaesthesia: A virtual reality study.

Body movements are invariably accompanied by various proprioceptive, visual, tactile and/or motor signals. It is therefore difficult to completely dissociate these various signals from each other in order to study their specific involvement in the perception of movement (kinaesthesia). Here, we manipulated visual motion signals in a virtual reality display by using a humanoid avatar. The visual signals of movement could therefore be manipulated freely, relative to the participant's actual movement or lack of movement. After an embodiment phase in which the avatar's movements were coupled to the participant's voluntary movements, kinaesthetic illusions were evoked by moving the avatar's right forearm (flexion or extension) while the participant's right arm remained static. The avatar's left forearm was hidden from view. In parallel, somaesthetic signals could be masked by agonist-antagonist co-vibration or be amplified (by agonist vibration only or antagonist vibration only) so that the real impact of visual cues of movement in kinaesthesia could be studied. In a study of 24 participants, masking the somaesthetic signals (which otherwise provide signals indicating that the arm is static) was associated with a greater intensity and shorter latency of the visually evoked illusions. These results confirm the importance of carefully considering somaesthetic signals when assessing the contribution of vision to kinaesthesia. The use of a combination of virtual reality and somaesthetic signal manipulation might be of clinical value.