TABLE OF CONTENTS There are a number of well-established "laws" that describe the simple, low-level control loops needed in tasks such as the visual control of hand position or the selection of an object on the screen.
Given an optimal state of readiness, with a finger poised over a button, a person can react to a simple visual signal in about 130 msec (Kohlberg, 1971). If the signals are very infrequent, the time can be considerably longer. Warrick et al. (1964) found reaction times as long as 700 milliseconds under conditions such that there could be as much as two days between signals. The participants were engaged in routine typing, so they were at least positioned appropriately to respond. If people are not positioned at workstations, their responses will naturally take longer.
Sometimes before someone can react to a signal, he or she must make a choice. A simple choice reaction-time task might involve pressing one button if a red light goes on and another if a green light goes on. This kind of task has been studied extensively, and it has been discovered that reaction times can be modeled by a simple rule called the Hick-Hyman law for choice reaction time (Hyman, 1953).
According to this law,
| (10.1) |  |
where C is the number of choices and a and b are empirically determined constants. The expression log 2 ( C) represents the amount of information processed by the human operator, expressed in...
