How does the Continuous Performance Test work?
Letters appear one at a time, one every 1 second, each shown for 300 ms. Press (tap anywhere, or Space) only when an X comes right after an A. Any other X, or an A followed by something else: don't press. There are 160 letters, about 2.7 minutes, and you aren't told right or wrong until the end.
Of the letters, 16 are targets (an X right after an A). 16 are X's after another letter and 16 are A's followed by something else, so pressing for every X, or on every A, gets caught out. The rest are other letters, never the same one twice in a row.
How is the Continuous Performance Test scored?
Your result is how many of the 16 targets you caught. Beside it are your misses, your false alarms (presses for anything else) and d′, a single score for telling targets from everything else: the higher, the better you did both at once. You also see how long you took, on average, to catch a target.
A press counts for the letter on screen; one within 100 ms of a new letter counts for the one before, since that is too soon to be a reaction to the new one. Only your first press on each letter counts. d′ uses the log-linear correction, adding half a press to each count, so even a perfect run has a finite score. Computed for some simple ways of playing:
| If you press for | Caught | False alarms | d′ |
|---|---|---|---|
| Exactly the targets | 16 | 0 | 4.59 |
| The targets, missing one | 15 | 0 | 4.05 |
| Every X | 16 | 16 | 3.10 |
| Nothing at all | 0 | 0 | 0.81 |
Where does the Continuous Performance Test come from?
H. Enger Rosvold and colleagues (1956) introduced it to study attention after brain damage. In one version people pressed for every X; in the other, the one used here, only for an X that followed an A. Many versions have been made since, including clinical ones with their own norms. This is a recreational version and gives no diagnosis.
Continuous Performance Test vs Go/No-Go Test
Both ask you to press for some things and not others, but the other way round. In the Go/No-Go Test you press for most shapes, so pressing becomes a habit and the test is stopping. Here you press for one letter in ten, so doing nothing becomes the habit and the test is noticing the moment that matters. The Vigilance Test takes that further: no letters at all, just waiting.
What can affect your Continuous Performance Test score?
Mind-wandering most of all: the letters keep coming whether you are with them or not, and a target missed in a daydream counts the same as any other miss. Tiredness, noise and interruptions add misses; hurrying adds false alarms. Leaving the page pauses the run, and the letters you couldn't see are left out of the score.