Fig 1.
Experimental setting (Fig 1a + Fig 1b). Fig 1a. Picture of the double mirror Alter Ego designed by Moritz Wehrmann. The experiment took place in a completely darkened enclosed space in the research centre of the Brest Hospital. The mirror was installed on a square table. The AN patient and his matched control sat facing each other on either side of the double mirror. Fig 1b. Schematic representation of the individuals during the recognition task. Both participants wore a black cape covering the neck, the whole chest and the arms so that only the face was visible. They were asked to look each other straight in the eye and to focus only on the other person’s face. Height-adjustable chairs allowed strict alignment of the eyes.
Table 1.
Clinical characteristics of participants with anorexia nervosa.
Fig 2.
Simultaneous alterations in light intensity on each side of the mirror over time (Fig 2a + 2b). Fig 2a. Light intensity over time.
- - At the beginning of the procedure, the light intensity was 100% for the HCs (mirror effect), whereas the light intensity was 0% for the AN patients (transparent window effect). -Then, the light intensity is progressively increased in 10% steps on the AN patient’s side while remaining at 100% for the HCs until 100% is reached on both sides.
- - During this first step, the AN patient’s image progressively appears and becomes increasingly fused with the HC’s image.
- - When both sides are at 100%, the light intensity is progressively decreased in 10% steps on the HC’s side, while it remains at 100% on the AN patient’s side.
- - During this step, the HC’s image progressively fades until its total disappearance when the light intensity drops to 0%.
- - Then, the reverse procedure is used to return to the initial configuration (100% on the HC’s side, i.e., a mirror effect for the HCs, and 0% on the AN patient’s side, i.e., transparent window effect for the AN patients).
- - Therefore, a condition with identical light intensities is presented twice to the participants during this sequence called one “passage back and forth”.
Fig 2b. Relative light intensity perceived by each participant over time. Relative light intensity perceived by the participants taking into account that modifications of light intensity on one side modifies its reflective properties on both sides.
Fig 3.
Synthesis of the experimental procedure during one “passage back and forth”.
During the task, the image the AN patient sees undergoes a morphing from other to self and then from self to the other. Simultaneously, the image the HC sees undergoes a morphing from self to other and then from other to self. The threshold M1 corresponds to the light intensity at which the perceptual shift from other to self occurs. The M2 threshold corresponds to the light intensity at which the perceptual shift from self to other occurs. The procedure is then repeated a second time. Thus, for each subject, 2 M1 and 2 M2 thresholds are obtained.
Table 2.
Comparison of the results for the recognition task between individuals with AN (N = 7) and Healthy controls (N = 7) in Neutral (Neu), Right hemi-body weighting (RHB), Left hemi-body weighting (LHB), Back- and Foot- Rest (BFR), Unstable Cushion (UC) and Neoprene (NP) conditions.
Fig 4.
Comparison of M1 and M2 levels in HCs and ANs in neutral condition.
This figure indicates that, in the HCs, the critical perceptual threshold corresponding to the ability to recognize self and other was the same regardless of the direction of morphing. In contrast, in the individuals with AN, this perceptual threshold varied depending on the direction of the morphing, and the shift from self to other or from other to self did not occur at the same threshold.
Fig 5.
Distribution of M1 and M2 in AN and HC in neutral condition.
Two points are superimposed.
Fig 6.
Distribution plots of M1 levels in AN and HC in Neutral (Neu), Right hemi-body weighting (RHB), Left hemi-body weighting (LHB), Back- and Foot- Rest (BFR), Unstable Cushion (UC) and Neoprene (NP) conditions.
Fig 7.
Distribution plots of M2 levels in AN and HC in Neutral (Neu), Right hemi-body weighting (RHB), Left hemi-body weighting (LHB), Back- and Foot- Rest (BFR), Unstable Cushion (UC) and Néoprene (NP) conditions.