Is that me or my twin? Lack of self-face recognition advantage in identical twins

Abstract

Despite the increasing interest in twin studies and the stunning amount of research on face recognition, the ability of adult identical twins to discriminate their own faces from those of their co-twins has been scarcely investigated. One's own face is the most distinctive feature of the bodily self, and people typically show a clear advantage in recognizing their own face even more than other very familiar identities. Given the very high level of resemblance of their faces, monozygotic twins represent a unique model for exploring self-face processing. Herein we examined the ability of monozygotic twins to distinguish their own face from the face of their co-twin and of a highly familiar individual. Results show that twins equally recognize their own face and their twin's face. This lack of self-face advantage was negatively predicted by how much they felt physically similar to their co-twin and by their anxious or avoidant attachment style. We speculate that in monozygotic twins, the visual representation of the self-face overlaps with that of the co-twin. Thus, to distinguish the self from the co-twin, monozygotic twins have to rely much more than control participants on the multisensory integration processes upon which the sense of bodily self is based. Moreover, in keeping with the notion that attachment style influences perception of self and significant others, we propose that the observed self/co-twin confusion may depend upon insecure attachment.

Fig 1. Experimental stimuli and procedure.

A) Example of the experimental conditions and stimuli for each trio (twin 1, twin 2, and control participant). Each twin was presented with the Self, the Twin and the Friend Face, while the control participant was presented with the Self and both the twins’ faces. Each key (1, 2, 3) was associated with one of the three identities (Control, Twin 1, Twin 2), regardless of the orientation (upright, inverted). Thus, in the represented trio, Twin-1 responded with key 1 for the Friend face, with key 2 for the Self-face and with key 3 for the Co-twin face. Twin-2 responded with key 1 for the Friend face, with key 2 for the Co-twin face and with key 3 for the Self-face. Control participant responded with key 1 for the Self-face and with keys 2 and 3 for the Twin-1 and Twin-2 faces, respectively. B) Schematic representation of one representative trial. A black screen with a white cross (1 sec.) preceded the display of one of the three faces (30 ms.), followed by a black screen (3 sec.), during which the subject had to respond which identity he/she had seen by pressing the associated response key. The individuals in this manuscript have given written informed consent (as outlined in PLOS consent form) to publish these case details.

Fig 2. Face recognition indices.

A) Results of separated repeated measures ANOVAs on Face Recognition performance (normalized inverse efficiency scores (IE), y-axis) scores are represented for both Twins (violet line) and Control (green line) participants as a function of observed Face Identity (x-axis). B) Results of mixed-model ANOVA comparing Twins (violet line) and Control (green line) Face Recognition performance (normalized inverse efficiency scores (IE) for mediated Twins faces; y-axis) as a function of Face Orientation (x-axis). Means and standard errors (SE) are represented. Asterisks indicate significant differences from Newman-Keuls post-hoc comparisons.

Fig 3. Correlations.

A) Perceived Similarity and B) Insecure attachment (Preoccupation with Relationship (PwR); “Relationship as Secondary” (RaS) subscales of the Attachment Scale Questionnaire) were found to significantly predict the absence of self-face recognition advantage (normalized inverse efficiency scores mediated for upright and inverted Self-face, x-axes) in twins.