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.
Highlights
Imagine that during your sleep you shrank to the size of a Barbie doll
What would happen if we could conduct an experiment like this? What if we could achieve a situation in a laboratory setting where people would experience a tiny body or a huge body as their own? How would they experience the world? In the present study we describe a series of novel experiments that examine this fundamental question
Despite the intuitive idea that the visual system creates a true image of the external world more or less like a video recorder based on retinal and oculomotor information, several theoreticians have suggested that visual perception of objects in the external world partly depends on how one could interact with those objects
Summary
Imagine that during your sleep you shrank to the size of a Barbie doll. Upon awakening, would you feel your body to be small, or would you sense that you were normal in a gigantic world inhabited by giants? This thought experiment illustrates the classical philosophical question of whether one’s own body size affects how we perceive the world [1,2]. The embodied cognition movement claims that the possible movement (or effort) one should make to interact with an object directly influences visual perception in a phenomenological manner [e.g. 18–20] In line with this idea are, for example, the findings that the perceived slope of a hill [21] and distances [22] appear larger when participants wear heavy loads. We carried out a series of experiments to investigate whether the size of the owned body influenced the perceived size and distance of objects presented in front of the participants (Experiments 6–10, see Table 1) In these experiments, participants received identical visual information in the illusion condition and a control condition, i.e. only the sense of ownership differed between otherwise equivalent conditions. Our results provide compelling support for the idea that the size of one’s own body directly influences the perception of the size of the entire external world
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