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Hand and arm representation in childhood

Fri, March 22, 3:00 to 4:30pm, Baltimore Convention Center, Floor: Level 3, Room 349

Integrative Statement

Our hands and arms mediate most of our interactions with the environment: they allow us to reach, move and manipulate objects while “collecting” information through the skin.
Given this crucial role in both the motor and perceptual domain, one might make the hypothesis that the brain contains a correct and veridical representation of both hands and arms. However, evidence from the adult literature says otherwise that body representations are distorted. Moreover, the same literature converges in showing that different body representations might exist and be accessed depending on the task to be performed and the sensory information provided.
Here we addressed the question of whether such distortions are present since childhood, if they change over time and whether they are independent on the task to be performed. Indeed, during the first decade of our life, our body undergoes tremendous modifications in size and shape that must be taken into account.
We conducted a series of studies in which a group of 84 children (between 6 and 10 years old) was asked to estimate, using different sensory modalities and response methods, their arm, and hand size.
In particular, we asked children to make explicit judgments about their hand size using either visual or tactile information (exp. 1), localize touch delivered to their fingertip, wrist, and elbow (exp. 2) and judge whether an object presented in front of them is reachable or not.
We found that both arm and hand representations are distorted in children too but in different ways. Hand size is underestimated in all tasks and modalities and such underestimation increases with age. Arm representation develops according to an opposite trend for which the underestimation decreases with time. Interestingly, arm length estimation does not correlate with reaching judgments as, despite representing their arm as shorter then it is, all children overestimate their ability to reach an object placed far from them.
These results suggest that body representations grow fragmented and distorted during childhood, with different body parts following different rules. Moreover, they support the notion proposed in the adult literature that multiple body representations exist to subserve different function (reaching, touch localization etc).

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