How many monkeys does it take to work out if rhesus macaques understand medians? According to researchers from the University of Padua, Italy, just two, as “Arrow” and “Tolman” proved themselves to be capable of some complex quantitative processing when looking at rows of dots in a recent study.
Published in the journal Biology Letters, the study set out to explore how far the numerical competence of rhesus macaques (Macaca mulatta) could stretch in testing if they could identify the numerical middle in a sequence. That’s to say, if you’re looking at a row of five ducks could you identify where the middle sits (the one with two ducks either side, FYI).
What they did
To do so, they set up Arrow and Tolman with touch-sensitive computer monitors that would reward them with food pellets when they got the answer right. They were shown a series of identical dots stretching from three to nine and would only receive the food reward when they selected the middle option.
To ensure they weren’t just getting used to tapping the same point on the screen, the researchers moved the dots around with each test. They also shifted the dots’ dispersal so that the numerical middle and the spatial middle were not the same, and correct answers couldn’t have been established without counting.
Could they do it?
Arrow and Tolman showed themselves to be very capable of establishing the numerical middle on a short dot stretch, but accuracy started to fall away the longer the sequences got. However, when they were faced with the numerical-spatial middle sequence tasks, both selected the former over the latter.
“The present study provides strong evidence that supports our previous finding that monkeys can identify the middle in sequences of discrete items and extends the findings in two important ways,” concluded the study authors.
“First, we show that monkeys transfer a middle rule learned with a small set of discrete items to a larger set of discrete items. Second, we demonstrate that despite having learned the middle rule with sequences for which spatial and numerical cues were confounded, monkeys abstracted numerical information only.”
What it all means
The findings tap into previous research involving five-day-old chicks which found they relied on numerical over spatial information in a container-pecking task. Combined, the studies provide insights into animal behavior in showing that numerical information is important for many species, and something that’s automatically taken into account even when other cues are available.
The study, while intriguing, is not without its limitations being focused on just two individuals which limits its generalizability to the wider rhesus macaque population. However, it adds to a growing body of research demonstrating that math isn't just something invented by humans to torture young students.
Who knows? Next week we could be bringing you news of slug Sudoku.