p406fig12.02 The Vector Integration to Endpoint, or VITE, model of arm trajectory formation enables the three S's of a movement to be realized: Synergy formation, Synchrony of muscles within a synergy, and variable Speed that is under volitional control (G).  This is accomplished by subtracting a present position vector (P) from a target position vector (T) to form a difference vector (V) which moves P towards T at a speed that is determined by G.<BR>||  The three S's of movement control.  T-> D [-> [[D]+G]-> P->], P-> D (inhib), G-> [[D]+G].<BR>1. Synergy - Defining T determines the muscle groups that will contract during the movement.<BR>2. Synchrony - When G turns on, all muscle groups for which D != 0 contract by variable amounts in equal time.  Because G multiplies D, it does not change the direction in which P moves to acquire T: straight line movement.<BR>3. Speed - P integrates D at rate G until P = T.  Increasing (decreasing) G makes the movement faster (slower).