If I only had bones: Some principles of behavioural organization derived from animals with skeletons (#192)
Most functionally organized actions need to be executed quickly, yet often there are many options available at each phase of the unfolding movement sequence that could, in principle, cause delays as the options are weighed. One source of constraint on the number of options provided in animals with skeletons (e.g., arthropods, vertebrates) arises from the skeletal articulation itself, where joints may only allow movements in a limited set of dimensions. However, even for animals with skeletons, while the range of movement may be curtailed, rarely are the movements available limited to one, thus, further constraints are needed. Even in simple functional actions, such as reaching, scratching and righting, there appear to exist neural rules that constrain which options are most likely to be used. Such rules serve to reduce the computational costs of sequencing movements and so facilitate their speedy execution. Some neural constraints may arise individually via habit formation or originate phylogenetically, but either way, sometimes speed is gained at the expense of efficiency. The costs of replacing less efficient actions may be greater than the cost of reduced efficiency, but such imperfections provide clues to the rules underlying behavioural organization. The lessons learned from animals with jointed skeletons may serve as useful guides to how animals with hydrostatic skeletons may lessen the degrees of freedom of movement in action construction.