Cognitive Tradeoff Theory - Tetsuro Matsuzawa

We then decided to make a direct comparison between the working memory of humans, adult chimpanzees, and young chimpanzees. The masking task was modified slightly for the purposes of this comparison. Sana Inoue, now an associate professor of Ritsumeikan University, and a postdoctoral student at that time, introduced the limited-hold task, in which the numerals were presented to the chimpanzees for only a brief duration.37 Suppose that there are five numerals—2, 3, 5, 8, and 9—displayed on the touch screen. After 650 milliseconds (ms), 430 ms, or 210 ms, all the numerals are automatically replaced by white squares. The goal is to touch the white squares in the ascending order of the now-masked numerals.

Ai’s performance in the limited-hold task was comparable to that of university students facing the same test for the first time. The performances of three young chimpanzees were much better than those of humans. We also tested the impact of overtraining among human subjects, allowing them to repeat the memory test many times over. Although their performances improved with practice, no human has ever been able to match Ayumu’s speed and accuracy in touching the nine numerals in the masking task.

One day, a chance event occurred that illustrated the retention of working memory in chimpanzees. While Ayumu was undertaking the limited-hold task for five numerals, a sudden noise occurred outside. Ayumu’s attention switched to the distraction and he lost concentration. After ten seconds, he turned his attention back to the touch screen, by which time the five numerals had already been replaced with white squares. The lapse in concentration made no difference. Ayumu was still able to touch the squares in the right order. This incident clearly shows that the chimpanzee can memorize the numerals at a glance, and that their working memory persists for at least ten seconds.

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In 2013, I proposed the cognitive tradeoff theory of language and memory. Our most recent common ancestor with chimpanzees may have possessed an extraordinary chimpanzee-like working memory, but over the course of human evolution, I suggested, we have lost this capability and acquired language in return. Suppose that a creature passes in front of you in the forest. It has a brown back, black legs, and a white spot on its forehead. Chimpanzees are highly adept at quickly detecting and memorizing these features. Humans lack this capability, but we have evolved other ways to label what we have witnessed, such as mimicking the body posture and shape of the creature, mimicking the sounds it made, or vocally labeling it as, say, an antelope.

- Primate Memory, Tetsuro Matsuzawa