Where is your head? Perception of relative position of the head on a wielded object.

Perception of exteroceptive properties (e.g., object length) by effortful or dynamic touch is both task-specific and anatomically independent. We investigate whether task-specificity and anatomical independence generalize to perception of proexteroceptive properties of the person-object system (i.e., relative position of the body on a wielded object). Moreover, we do so when objects are wielded by a body part that is unlikely to be well practiced in such tasks-the head. Experiment 1 found that participants can perceive the relative location of the head on a wielded object and that such perception is likely supported by task-specific sensitivity to an invariant mechanical stimulation pattern-rotational inertia. Experiment 2 found that participants have at least some ability to differentiate between this property and a related exteroceptive property (i.e., partial length of a wielded object extending to one side of the head). The results are discussed in terms of information for perception by effortful touch and a description of the haptic system as a biotensegrity structure.