Rubber hand illusion paradigm

Testing was conducted in a climate-controlled room. In the rubber hand illusion task, the participant’s right arm was placed in a box (86 cm×60 cm×20 cm), screened from view. A life-size artificial ‘rubber’ model of a right hand was placed midline within the visible section of the box, directly in front of participant body. The distance between the participant’s right index finger and the index finger of the rubber hand was 20 cm.

Stroking with a paintbrush was applied by the experimenter (VB) to the index finger of the participant’s hidden hand and the artificial hand. Two conditions were performed in a counterbalanced order across participants: 1) Synchronous stroking when the timing of the brush strokes on the participant’s own hand and on the rubber hand was coincided. 2) Asynchronous stroking when the timing of the brush strokes on the participant’s hand and rubber hand was out of phase by approximately 625ms). Each condition lasted two minutes. At the beginning of each condition, the participant estimated the location of her/his right index fingertip three times by reading the corresponding number along a one-meter ruler, whose visible position varied each time to prevent the participant repeating responses in subsequent readings. Post-induction finger location judgements were obtained in the same manner as prior to the induction. Proprioceptive drift was calculated by subtracting the average of the pre-induction finger location judgements from the average of post-induction finger location judgement:

After each condition, the participant completed the RHI questionnaire comprising 10 items divided into three subscales: ownership, location, and agency, see Table 1 for further details. The items were measured on a 7-point Likert scale (1 = strongly disagree, 7 = strongly agree) and the average score for each subscale was calculated [33].

(See [33]).