15-4. Sensory/Motor Signals and Forward/Inverse Models

The basic structures of forward- and inverse-model-based control systems are shown schematically in Figures 8, 43, and 44. To discuss how they differ in their operation, one must realize that instruction and sensory signals represent movement in spatial coordinates—that is, the description of motion of the body, or its various parts, in terms of position, velocity, acceleration, and direction (termed “kinematics”). In contrast, motor signals commanding movements are represented in bodily coordinates—that is, the description of motion that includes force as the cause of motion (termed “dynamics” or “kinetics”). In this volume, we prefer “dynamics” as it is used widely in internal-model-based control of a robot manipulator (An et al., 1988). In simple control systems, these two types of coordinates can be approximately identical; for example, for the VOR, the spatial coordinates determined by the semicircular canals parallel the bodily coordinates determined by the activation of extraocular muscles (Ezure and Graaf, 1984a; Chapter 10, “Ocular Reflexes”). In complex control systems, however, such as those required for multijoint arm/hand/finger movements, the bodily coordinates are complex and clearly distinct from spatial coordinates. Therefore, sensory and motor signals need to be represented in their spatial and bodily coordinates, respectively, but not in their admixture. Here, we address the question of what rules determine the sensory/motor nature of mossy and climbing fiber information, and the nuclear output of a microcomplex.