Schemas for the temporal organization of behaviour.

Those aspects of the timing of behaviour are emphasized which derive from the need for the organism to coordinate its actions with objects in the environment. Such coordination may require the serial performance of certain actions, yet permit elements of concurrency as well. Perceptual and motor schemas are introduced as units for the functional description of behaviour intermediate between a purely phenomenological description and an account of the detailed neural mechanisms of behaviour. The language of coordinated control programs is outlined to suggest how such schemas are orchestrated in visually and tactilely guided behaviour. Finally, a crucial property of the timing of many movements is discussed: their division into a fast (feedforward, ballistic) phase followed by a slow (feedback) phase. This division is analyzed in the light of the effect of brain damage on reaching movements.