Stimulus information as a determinant of reaction time.

In the typical reaction-time experiment, S's reaction time is greater when he has to respond differentially to one of two equally probable stimuli instead of to just one stimulus. In fact, Merkel (2), using one to ten alternatives, has demonstrated that when S has to respond to one stimulus chosen from a number of equally probable alternatives, his reaction time increases with the number of alternatives. The fact that S's response to stimulus A takes more time when A is one of several rather than one of two equally probable alternatives is of intrinsic interest. But it becomes even more significant when looked at from the standpoint of modern communication theory. In communication theory the amount of information which a message conveys is an increasing function of the number of possible messages from which that particular message could have been selected. The S's reaction time seems to behave,