Simple vs Choice Reaction Time, and Hick's Law
In 1868 a Dutch physiologist called Franciscus Donders had a clever idea. He couldn't look inside anyone's head, but he could time them. If he measured how long people took to respond to a light, and then how long they took when they first had to work out which light it was, the difference should be the time it takes to make a decision. Psychologists still split reaction time up the way he did.
Donders' three tasks
The simple version is the one you play on this site. One signal, one response. You know what's coming and what to do, so the only question is how quickly your nervous system can get from "see it" to "move".
The choice version adds a decision. Two lights, two buttons: left light means left button, right light means right button. Now you have to identify the signal and pick the matching response before you can move, and that reliably takes longer.
The third version sits in between. Two possible lights but only one button; you press for one light and do nothing for the other. You still have to identify the signal, but there's no choice of response to make. It's sometimes called a go/no-go task, and you've played one if you've ever tapped only the green items in a phone game while avoiding the red ones.
Every extra option costs you (Hick's law)
In 1952 the British psychologist William Hick asked what happens as you keep adding choices. His answer, confirmed a year later by the American Ray Hyman, became known as Hick's law: reaction time grows with the logarithm of the number of options, not the number itself.
In practice that means each doubling of the options adds roughly the same extra time. Going from two choices to four slows you down by about as much as going from four to eight. People manage this because they don't check every option one at a time; they narrow the field in chunks, a bit like a game of twenty questions. It's also why the first extra choice hurts the most. Going from one option to two adds a whole decision where previously there was none.
Hick's law turns up well outside the lab. Interface designers use it to argue for shorter menus. It's also a neat way to think about "reading the play" in sport: an experienced player who can rule out half the possibilities early is effectively facing fewer choices, so they decide faster.
Why this game only has one target
A choice task measures two things tangled together: raw speed and decision strategy. Some people rush and make mistakes; others slow down to be sure. That trade-off between speed and accuracy is interesting in its own right, but it makes scores hard to compare, because two players with identical reflexes can get very different results.
Keeping the test simple strips all of that out. There's one target type, it only appears after a random wait, and you can only hit it by tapping or clicking it. Your score is about as close to pure speed as a browser can measure, which is what makes a leaderboard fair.
Choice reaction time ages differently
A large UK survey of more than 7,000 adults, reanalysed by Geoff Der and Ian Deary in 2006, found that simple reaction time barely changed until people reached their fifties. Choice reaction time was different: it slowed steadily across the whole adult age range. The extra decision step seems to be the part that ages first. There's more on this in reaction time by age.
Sources
- Donders, F. C. (1868/1969). On the speed of mental processes. Translated by W. G. Koster. Acta Psychologica, 30, 412–431.
- Hick, W. E. (1952). On the rate of gain of information. Quarterly Journal of Experimental Psychology, 4(1), 11–26.
- Hyman, R. (1953). Stimulus information as a determinant of reaction time. Journal of Experimental Psychology, 45(3), 188–196.
- Der, G., & Deary, I. J. (2006). Age and sex differences in reaction time in adulthood. Psychology and Aging, 21(1), 62–73.