Have a look at this video. (N.B. it is played back at normal speed)
After the numbers 1 through 9 make a split-second appearance on a computer screen, the chimp, Ayumu, gets to work. His index finger moves quickly across the screen, tapping white squares where the numbers had appeared, in order. Ayumu’s talent caused a quite a stir when researchers first reported it (Matsuzawa, 2009).
In an upcoming Trends in Cognitive Sciences essay, Nicholas Humphrey floats a different explanation for Ayumu’s superlative performance: Ayumu might have a curious brain condition that allows him to see numbers in colors. A simple experiment could reveal whether Ayumu is synesthetic: Changing the white square to colored squares would throw him off if he was relying on colors to order the numbers. According to ScienceNews Matsuzawa, who declined to comment directly on Humphrey’s theory, has no plans to test this.
Nicholas Humphrey (2012). ‘This chimp will kick your ass at memory games – but how the hell does he do it?’ Trends in Cognitive Science DOI: 10.1016/j.tics.2012.05.002
Tetsuro Matsuzawa (2009). Symbolic representation of number in chimpanzees Current Opinion in Neurobiology, 19 (1), 92-98 DOI: 10.1016/j.conb.2009.04.007