Response Timing Accuracy of Long-Distance Movements

The inverse relationship between movement speed and movement accuracy is mathematically represented byFitts' law (Fitts, 1954) and has been confirmed across a range ofmovement conditions and populations (Kerr, 1973; York & Biederman, 1988). It has been reported, however,that the relationship does not hold when the response demands require timing accuracy as opposed to spatial accuracy (Newell, 1980). Using a curvilinear and a rotary (hand crank) positioning device in two separate experiments,jasiewicz and Simmons (1996) reported that timing variability (as indexed by variable error; VE) decreased as movement velocity increased, whereas directional bias (indicated byconstant error; CE) remained relativelystable about the criterion target They also established that completing short movements at slow velocities resulted in significantly smaller VE than when the same velocities were maintained during medium or long movements (Simmons & Williams, 1994). This distance effect wasreduced asvelocityincreased, even at the longest distance tested (720°), with the hand crank. The results suggested that directional timing accuracy (CE) and variability (VE) are independent of movement distance at high velocities (i.e., a distance effect). What remains unclear iswhether the distance effect continues to decrease with longer movements. Using the same freely