Effects of noise on a delayed visual feedback system.

Experimentally it is known that some patients with Parkinson's disease are not able to use visual information in a normal manner in a simple motor tracking task involving a time delay. We considered the possibility that pathological tremor present in these individuals acts as noise and prevents them from performing normally. To test this hypothesis the effects of adding coloured noise was investigated experimentally and theoretically. Ten adult subjects with no known neurological disease were asked to track their own delayed finger position with different levels of coloured noise and delays introduced. Also, a model for the task utilizing first-order delay-differential equations was constructed and coloured noise was injected into simulations. The theoretical implications of the inclusion of a stochastic component are considered, and the prospect of the dynamics being driven by noise is discussed. Experimental and numerical results indicate that augmented noise tends to corrupt and curtail the oscillations normally induced by time delays. This augmented noise may explain why some patients with Parkinson's disease are not able to utilize visual information in a normal manner.