Being Barbie: the size of one's own body determines the perceived size of the world

Abstract

A classical question in philosophy and psychology is if the sense of one's body influences how one visually perceives the world. Several theoreticians have suggested that our own body serves as a fundamental reference in visual perception of sizes and distances, although compelling experimental evidence for this hypothesis is lacking. In contrast, modern textbooks typically explain the perception of object size and distance by the combination of information from different visual cues. Here, we describe full body illusions in which subjects experience the ownership of a doll's body (80 cm or 30 cm) and a giant's body (400 cm) and use these as tools to demonstrate that the size of one's sensed own body directly influences the perception of object size and distance. These effects were quantified in ten separate experiments with complementary verbal, questionnaire, manual, walking, and physiological measures. When participants experienced the tiny body as their own, they perceived objects to be larger and farther away, and when they experienced the large-body illusion, they perceived objects to be smaller and nearer. Importantly, despite identical retinal input, this "body size effect" was greater when the participants experienced a sense of ownership of the artificial bodies compared to a control condition in which ownership was disrupted. These findings are fundamentally important as they suggest a causal relationship between the representations of body space and external space. Thus, our own body size affects how we perceive the world.

Figure 1. Experimental set-up.

This figure displays the main experimental set-up (A), the four artificial bodies (B), and the image seen by participants during visuo-tactile stimulation (C), the Barbie doll experiment (D), object size estimation (E), and distance estimation (F).

Figure 2. Results of Experiments 1–4: Illusory ownership of tiny and huge artificial bodies.

Average scores on illusion statements and control statements (see Table S1) after synchronous and asynchronous touching of small body (A) and large body (B), and average threat-evoked SCR after a period of synchronous and asynchronous touching of the small body (C) and the large body (D). * p<0.05, *** p<0.001. Error bars indicate SEM.

Figure 3. Results of Experiment 5: Illusory ownership of the body of a Barbie doll.

Average scores for illusion statements, control statements and statements regarding the size of seen objects (see Table S1). ** p<0.01, *** p<0.001. Error bars indicate SEM.

Figure 4. Results of Experiments 6–8: Own body size effect on size perception.

The body size effect on verbal size estimation (A) and hand aperture (B) as a percentage deviation from the average estimation of all trials and the effect of the ownership illusion on hand aperture as a percentage deviation from corresponding asynchronous condition (C). * p<0.05, ** p<0.01, *** p<0.001. Error bars indicate SEM.

Figure 5. Results of Experiments 9 and 10: Own body size effect on distance perception.

The body-size effect on verbal distance estimation as a percentage deviation from average estimations (A) and as percentage deviation from the corresponding asynchronous condition (B). The body-size effect on walking distance as a percentage deviation from average estimations (C) and as a percentage deviation from the corresponding asynchronous condition (D). * p<0.05, ** p<0.01, *** p<0.001. Error bars indicate SEM.