Colour Count Test

A 4 × 4 grid of keys lights up in red, green, blue and yellow for a moment, then every key turns into a jumble of all four colours, then grey. Before each pattern you are told what to look for: the colour there was most of, or the colour there was least of. Then pick it from the four.

The pattern is shown more briefly when you are right and longer when you are wrong, homing in on the time you need to be right 80% of the time, separately for most and least. Guess when you are not sure; a guess is right 1 time in 4. Usually about 60 patterns, more if your answers vary; four to six minutes.

Judging which colour dominates a glimpse needs the whole display taken in at once, a measure of the speed and span of visual attention.