Ayumu, and how people caught up

In 2007, Sana Inoue and Tetsuro Matsuzawa of Kyoto University’s Primate Research Institute published a short paper in Current Biology called “Working memory of numerals in chimpanzees.” Its star was Ayumu, a young chimpanzee born in 2000, the son of Ai, a chimpanzee who had worked with numbers at the institute for many years. Videos of Ayumu went around the world, often with the caption “monkey.” Chimpanzees are apes, not monkeys.

What the chimpanzees did

The numerals 1 to 9 appeared at random places on a touch screen, and the chimpanzees had learned to touch them in order, smallest first. In the masking version, as soon as they touched the first numeral, the others turned into plain white squares, so the rest of the order had to come from memory. In the limited-hold version, five numerals showed for 650, 430 or 210 milliseconds and then turned into white squares. 210 milliseconds is about a fifth of a second.

Ayumu’s accuracy stayed about the same at all three times. Nine university students, tested with the same equipment and procedure, did worse as the time got shorter, and Ayumu beat them at 430 and 210 ms. The authors compared his skill to eidetic imagery, the vivid, picture-like memory that is more common in children than in adults.

Not every chimpanzee was a star. Ayumu’s mother, Ai, scored below the students’ average, and Ayumu was the only one of the six chimpanzees in the project to reach his level.

Practice made the difference

Ayumu had practiced number tasks on the touch screen for a long time before the test; Peter Cook and Margaret Wilson describe about 200 trials a day, five or six days a week. The students had tried the task in a single session. So other researchers gave people practice:

• Alan Silberberg and David Kearns (2009) found that two people who practiced the task matched Ayumu’s accuracy.
• Cook and Wilson (2010) trained two university students at 650 ms for about 15,000 trials. Before practice they got 38% and 46% right at 210 ms; afterward, 94% and 96%, which Cook and Wilson report as better than Ayumu.
• A larger online study (Roberts and Quillinan, 2014) also found that practice helps people a great deal, but suggested the chimpanzees may still have the edge when seven or more numbers appear at once.

So was the video debunked?

Not really. Ayumu’s memory was real and remarkable, and the video was not faked. What the follow-up studies showed is that the first comparison was uneven: a well-practiced chimpanzee against people trying the task for the first time. With practice, people can match or beat him. That is what this game is for: a ladder like the one Ayumu climbed, from numbers that wait for your first touch down to the study’s 210 milliseconds.

Steps 7, 8 and 9 of the ladder use the study’s five numbers and its three display times, and the study’s test mixes ten trials at each. Screens, fingers and browsers vary, so treat your scores as your own yardstick, not a lab result.

Sources

1. Inoue, S., and Matsuzawa, T. (2007). “Working memory of numerals in chimpanzees.” Current Biology 17(23): R1004–R1005. doi:10.1016/j.cub.2007.10.027; summary at the Primate Research Institute.
2. Silberberg, A., and Kearns, D. (2009). “Memory for the order of briefly presented numerals in humans as a function of practice.” Animal Cognition 12(2): 405–407. doi:10.1007/s10071-008-0206-8
3. Cook, P., and Wilson, M. (2010). “Do young chimpanzees have extraordinary working memory?” Psychonomic Bulletin & Review 17(4): 599–600. doi:10.3758/PBR.17.4.599
4. Roberts, S. G., and Quillinan, J. (2014). “The Chimp Challenge: Working memory in chimps and humans.” In The Past, Present and Future of Language Evolution Research, 31–39. Summarized in Wikipedia’s Cognitive tradeoff hypothesis.
5. Wikipedia, Ayumu (chimpanzee).