When they touched the first digit, the others were replaced with white squares, and they had to rely on their memory to press the right sequence. The young chimps took to this task particularly well and amazingly, they finished the task more quickly than human adults...
When the numbers were flashed for two thirds of a second, Ayumu's skills were the equal of 6 university students who pressed the right sequence 80% of the time. If the numbers were displayed for just a fifth of a second, the students couldn't cope. They didn't have enough time to make a single saccade, the small eye flickers that we make when we scan a page or image. Without the luxury of exploring the screen, the students only answered accurately 40% of the time. Ayumu, on the other hand, wasn't fazed and maintained his earlier high scores.
The researchers also postulate that human children may have similar eidetic abilities when they are very young, but lose this capacity by the time they finish school. Or something like that - I can't remember.