As a basis for understanding the visual system, we need to consider the functions that vision has to perform, which are pre-eminently in the service of activity, and the circumstances in which it normally operates, namely when the head is moving. The fundamental ecological stimulus for vision is not a camera-like time-frozen image but a constantly changing optic array or flow field, the description of which must be in spatio-temporal terms. A mathematical analysis of the optic flow field is presented, revealing the informamtion that it affords for controlling activity - information both about the topography of the environment and about the movement of the organism relative to the environment. Results of human behavioral experiments are also reported. It is suggested that the optic flow field should be the starting point in attempting to discover the physiological workings of the visual system.

In this report we explore the guidance of circumnutation of climbing bean stems under the light of general rho/tau theory, a theory that aims to explain how living organisms guide goal-directed movements ecologically. We present some preliminary results on the control of circumnutation by climbing beans, and explore the possibility that the power of movement in plants, more generally, is controlled under ecological principles.

A theory of action control (General Tau Theory) is applied to analyzing normal and abnormal movements in PD; and to designing and testing the efficacy of a sonic aid for PD. A central aspect of the theory, which is supported by experimental evidence across a variety of actions and species, is that the trajectories of competent skilled actions follow a particular temporal pattern, which is described by the mathematical function, tauG. Since tauG-control of actions can be largely deficient in PD, we designed a device that generates whoop-like sounds, where the fundamental frequency of the sound follows the tauG pattern. Our hypothesis was that by listening to these sounds the nervous system of someone with PD might be helped subsequently to self-generate tauG patterns in their nervous system, which might facilitate movement control in different situations. Five adults with PD, and five age-matched controls, took part in the study. They each listened to the sounds under two conditions: (a) experimental -turning a handle for 5 minutes while the sounds were played (b) control -turning the handle without the sounds. Before and after each condition, the tauG-control of lateral body sway while standing was measured (without the sounds playing), using force-plates, on two tasks: (i) keeping the feet down, (ii) lifting the trailing foot. The number of participants out of five, who showed greater ratio improvement following practice with whoop sounds compared to without sounds, was, on each task, high for the PDs compared with the agematched controls (4 vs 2 or 3). Thus, for the PDs, listening to the tauG whoop-like sounds while performing one action (handle turning) improved subsequent tauG-control on a different task (body-swaying).