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. 2020 Aug 26;23(9):101429. doi: 10.1016/j.isci.2020.101429

Figure 1.

Figure 1

Procedure

(A) Induction of the friend-body-swap illusion and visuotactile stimulation in the control conditions. The participants—a pair of friends (pink and green jumpers)—lay on two beds and wore two sets of head-mounted displays (HMDs). The recordings shown in the HMDs came from two digital cameras placed just above and behind each participant's head. This created high-quality 3D movies of either the friend's body (syncF, asyncF) or one's own body (syncS, asyncS) shown from a first-person perspective. At the same time, the experimenters applied strokes to the participants' bodies; the location, onset, and duration of each stroke were precisely controlled by audio cues heard by the experimenters. In the synchronous conditions, the touches seen in the HMDs and the touches felt on one's actual body were matched, whereas in the asynchronous conditions, the displays were delayed 3 s, creating a visuotactile mismatch.

(B) Illusion questionnaire. After each condition, the participants rated illusion (I1:I3) and control (C1:C4) statements on a 7-point scale (−3 “strongly disagree”; +3 “strongly agree”).

(C) Knife threats. Genuine ownership of the friend's body should be associated with increased physiological stress responses when this body is physically threatened. Thus, during each condition, we simultaneously “attacked” both participants' bodies with mock knives and measured skin conductance responses during these events.

(D) Friend rating and self-rating tasks. At the beginning of the study, before any body perception manipulation was applied, the participants listened to 120 trait adjectives and rated how well each trait described their friend (1 “not at all”; 9 “very much”). The same traits were then randomly assigned to the four full-body illusion conditions, and during each condition, the participants rated how well each trait described themselves.

(E) Timeline. Condition order was randomized across participants. The break between friend- and self-rating tasks was ~10 min; during this time, the full-body illusion setup was prepared.