Was always fascinated by these studies!
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.
I still remember this video about it from almost a decade ago:
