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A working memory test of chimpanzees, described in this BBC Earth video, shows a chimpanzee outperforming a human.

Another video shows a chimpanzee performing the test:

Young chimpanzees outperform human adults in a memory test. First, the chimpanzees learned to touch Arabic numerals from 1 through 9. Then, a memory test was introduced. After touching the numeral 1, the other numerals turned into white rectangles. The chimpanzees have to remember which numeral appeared in which location. We compared humans and chimpanzees in the same test.

It cites Matsuzawa et al., Current Biology 17(23), R1004-R1005.

The chimpanzee in the second video clip is certainly performing the task with a speed and accuracy that would be impressive for a human.

My question, however, is whether variations of this test have been carried out in order to rule out alternative explanations. In particular, if the numbers did not disappear, then the task would be enormously easier, and I'm wondering whether there is some artifact of the screen and/or the chimpanzee's visual system which means that that chimpanzee can still "see" the numbers after they have supposedly disappeared from the screen.

The basic reference in this subject seems to be:

Numerical memory span in a chimpanzee, by Nobuyuki Kawai and Tetsuro Matsuzawa, Nature volume 403, pages 39–40.

It has been cited many times, but I'm not sure how to search for the answer to the specific question I'm asking here.

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  • Did you mean to post this on Biology, Medical Sciences or perhaps Psychology & Neuroscience? Commented Apr 2 at 20:02
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    @JiminyCricket. I believe that, by the usual standards of the sciences in question, the paper I cited settles the question in the affirmative. In effect, I'm asking for a higher standard of proof than is usual. Compare, for example, the 1937 experiments by Young on rats in mazes, as described by Richard Feynman. Young was careful to enforce stronger controls than most experimenters did, to make sure he was drawing correct conclusions. Therefore I think my question is more suitable here than on those other sites. Commented Apr 2 at 20:24
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    There's something wrong with your references. The first link points to Sakai et al. (2011) "Differential prefrontal white matter development in chimpanzees and humans", but the label suggests that it was probably meant to point to Inoue & Matsuzawa (2007) "Working memory of numerals in chimpanzees". Can you sort this out?
    – Schmuddi
    Commented Apr 3 at 13:55
  • There would be a lot of variation within people too. For instance I don't have sensory recall (see Blake Ross's description of aphantasia ), so it would be impossible for me to ever complete this task, regardless of the time allowed. If there were far fewer numbers, I might manage it occasionally. At the other end of the scale, some people can glance at something and then recall the image in detail (perhaps only for a few seconds, or minutes, or for life). Commented Apr 3 at 16:20
  • @Schmuddi Those edits were not made by me, so I'm not sure what to do. Commented Apr 6 at 14:00

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It's not terribly clear to me what your question really is, but there are various types of memory. What is suspected is that the Japanese tests in question are in fact a test of eidetic (aka photographic) memory, and not of working memory (WM), but this is based on "anecdotal evidence" that performance in those Japanese tests was not affected by attentional interference like most WM tests are (e.g. having to recall which physical boxes in a set have been searched for food).

Previous studies focusing on WM performance in chimpanzees used serial learning paradigms in which participants learn to touch an array of stimuli in order (e.g. Arabic numerals) through extensive, step-wise training. Following this training, the array was masked once the subjects touched the first numeral in the sequence [38,39]. One juvenile chimpanzee mastered this masking condition with nine numerals on the screen. When chimpanzees were exposed to the stimuli for a predefined time interval before each trial (210–650 ms) [39], the shortest exposure time of 210 ms did not impair the performance of the best-performing juvenile (with five numerals on the screen). The authors suggested that apes' performance in this study might be based on an eidetic memory strategy [40], the ability to recall an image after only a brief moment of exposure. Similarly, Carruthers [6] argued that chimpanzees performance in this case might reflect a form of sensory short-term memory. Important task demands that distinguish short-term memory tasks from WM tasks, such as resistance to attentional interference (induced, for example, by a secondary task) or the continuous updating of memory contents, were not part of the research design. However, anecdotal evidence suggested that chimpanzees’ performance in this task was not susceptible to attentional interference [38,39].

Anyhow, in the food boxes search types of test, some chimpanzees exceed the (WM) ability of the average 7-year old human child. (Same source.) And since the latter kind of test doesn't use any screens...

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