Simple & Choice Reaction Time

Background

Reaction time (RT) — the interval between a stimulus and the response to it — is one of the oldest measures in experimental psychology. Franciscus Donders (1868) introduced the subtraction method, comparing simple RT (one stimulus, one response) with choice RT (multiple stimuli, each requiring a different response) to estimate the time needed for mental processes like discrimination and selection.

Hick's Law

William Hick (1952) and Ray Hyman (1953) showed that choice RT increases logarithmically with the number of alternatives: RT = a + b × log₂(n), where n is the number of equally probable alternatives. This is known as Hick's Law (or the Hick-Hyman Law).

What to Expect

Typical simple RT for a visual stimulus is 200–300 ms. Choice RT with 2 alternatives is typically 50–100 ms slower than simple RT. These times vary with alertness, practice, and stimulus intensity.

Your Task

In the simple RT block, press Space as fast as possible when the green circle appears. In the choice RT block, press F for green and J for blue circles.

References

Donders, F.C. (1868/1969). On the speed of mental processes. Acta Psychologica, 30, 412–431.

Hick, W.E. (1952). On the rate of gain of information. Quarterly Journal of Experimental Psychology, 4, 11–26.

Hyman, R. (1953). Stimulus information as a determinant of reaction time. Journal of Experimental Psychology, 45, 188–196.

Luce, R.D. (1986). Response Times: Their Role in Inferring Elementary Mental Organization. Oxford University Press.

This experiment measures your reaction time in two conditions:

Block 1 — Simple RT (20 trials): A green circle will appear after a random delay. Press Space as fast as you can when you see it.

Block 2 — Choice RT (40 trials): Either a green or blue circle will appear. Press F for green and J for blue as fast and accurately as possible.

Responses faster than 150 ms will be flagged as anticipations. Responses slower than 1500 ms will be flagged as lapses.

Keep your fingers on the response keys and focus on the center of the screen. A fixation cross (+) will appear before each stimulus.

Simple & Choice Reaction Time

Your Results