The role of haptic information in shaping coordination dynamics: Inertial frame of reference hypothesis

Current research suggests that non-visual perception of the spatial orientation of body segments is tied to vectors representative of their mass moment distribution (vmm). Our question was whether the relative orientation of vmm of right and left hands (Δvmm = vmm left − vmm right) constitutes haptic information supporting bimanual coordination and, if so, how it contributes to coordination dynamics. Blindfolded participants coordinated the motions of a pair of cross-shaped, hand-held pendulums that were either symmetrically loaded (Δvmm = 0) or asymmetrically loaded (Δvmm ≠ 0). The sign and magnitude of Δvmm, in particular of the first moment vector, systematically affected the pattern of coordination (indexed by mean relative phase ϕ), but not its stability. These results suggest that (1) Δvmm specifies a frame of reference about which coordination is organized; and (2) that the changes in pattern were a function of the experimentally induced biases in this perceptual frame of reference and not a function of a functional asymmetry akin to detuning. The implications of the findings to the understanding of perceptual regulation of interlimb coordination were discussed.

► We manipulate candidate inertial parameters informative of relative hand position.
► Bimanual patterns were a function of relative orientation of first moment vectors.
► Coordination stability was invariant over observed changes in pattern.
► Bimanual patterns are organized about an inertial frame of reference.