The role of hand size in body representation: a developmental investigation

Abstract

Knowledge of one's own body size is a crucial facet of body representation, both for acting on the environment and perhaps also for constraining body ownership. However, representations of body size may be somewhat plastic, particularly to allow for physical growth in childhood. Here we report a developmental investigation into the role of hand size in body representation (the sense of body ownership, perception of hand position, and perception of own-hand size). Using the rubber hand illusion paradigm, this study used different fake hand sizes (60%, 80%, 100%, 120% or 140% of typical size) in three age groups (6- to 7-year-olds, 12- to 13-year-olds, and adults; N = 229). We found no evidence that hand size constrains ownership or position: participants embodied hands which were both larger and smaller than their own, and indeed judged their own hands to have changed size following the illusion. Children and adolescents embodied the fake hands more than adults, with a greater tendency to feel their own hand had changed size. Adolescents were particularly sensitive to multisensory information. In sum, we found substantial plasticity in the representation of own-body size, with partial support for the hypothesis that children have looser representations than adults.

Figure 1

Procedure. Baseline: eyes closed, pointing under table to hand (inset). Illusion: stroking with brushes. Post-illusion pointing: eyes closed, pointing under table to hand (inset). Illusion & post-illusion points repeat (see “Methods”). Affordance: judging the size of an aperture the hand can fit through. Questions (see “Methods”). Fake hand for illustration only—see Fig. 2 for actual hands used.

Figure 2

Fake hands. To illustrate the appearance of the fake hands, this figure shows the set used for 6–7-year-olds. A corresponding second set was used for the other two groups.

Figure 3

Touch referral. This figure shows the medians and interquartile ranges of ratings on the questionnaire item regarding touch referral to the fake hand. Ratings are shown for each age group, fake hand size, and condition.

Figure 4

Ownership. This figure shows the medians and interquartile ranges of ratings on the questionnaire item regarding ownership of the fake hand. Ratings are shown for each age group, fake hand size, and condition.

Figure 5

Hand felt larger. This figure shows the medians and interquartile ranges of ratings on the questionnaire item regarding one’s own hand feeling larger following the illusion. Ratings are shown for each age group, fake hand size, and condition.

Figure 6

Hand felt smaller. This figure shows the medians and interquartile ranges of ratings on the questionnaire item regarding one’s own hand feeling smaller following the illusion. Ratings are shown for each age group, fake hand size, and condition.

Figure 7

Affordance judgment. This figure shows the means and standard errors of affordance judgments, for each age group, fake hand size, and condition.

Figure 8

Proprioceptive drift. This figure shows the mean and standard errors of the proprioceptive drift measure, for each age group, fake hand size, and condition.