Chimps don't like short measures: Official

Barmen beware a 'folk understanding of the physics of liquids'

By Lester Haines, 23rd February 2010

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Barmen should be warned that chimps have demonstrated a "folk understanding of the physics of liquids" which enables them to tell the difference between a full pint and a short measure.

According to research by psychologist Dr Michael Beran of Georgia State University, the animals can distinguish "continuous quantities" of liquids which simply get bigger as more liquid is added.

This is a different skill to their previously-demonstrated ability to tell apart "discrete quantities", such as "how many sweets are in a container", as the BBC puts it. In this case, chimps keep track of the total by "performing simple addition and subtraction calculations" as sweets are added or taken away, which allows them to discern that five is, for example, less than eight.

In the case of liquids, though, they need to deploy more advanced reasoning, so Beran set out to find out "whether they would perform as well when they had to judge two poured amounts of juice".

In the first experiment, a 37-year-old female called Lana, a 21-year-old female called Panzee and a 34-year-old male called Sherman watched while Beran poured quantities of fruit juice from an opaque 600ml syringe into two opaque cups, varying the amount injected into each.

Irrespective of the amount poured into each cup, "more than three quarters of the time", his subjects would select the cup containing the larger volume of juice.

In the second experiment, Bern presented the chimps with a quantity of juice "visible the entire time in a clear container", and then poured a second amount from an opaque syringe into an opaque cup.

This prevented the animals taking the "relatively easy option of timing the pouring events, and choose whichever cup had liquid poured into it for longer". Beran noted: "This is a complicated feat because there are no cues such as duration of pouring or height of the liquid that can be used. They must represent and compare the poured amount to the visible amount, and estimate which is larger."

Once again, Lana, Panzee and Sherman passed "with flying colours".

In the third test, "the heights at which the opaque syringes were held above opaque containers differed for each set, so that sometimes sets with smaller amounts of juice were dropped from a greater height, providing a possible visual illusion as to the total amount".

Beran explained: "I wanted to see whether the chimps overestimated the amount of juice if it was poured from higher up. This is an old favourite of the experienced bartenders of the world, where the patron gets the impression of getting more alcohol than is really true because of varying the height of the pouring."

The chimps were having none of it, and picked the largest measure "over 80% of the time".

Beran's abstract in the journal Animal Cognition concludes: "Chimpanzees succeeded in all tasks and showed many similarities in their continuous quantity estimation to how they performed previously in similar tasks with discrete quantities.

"Chimpanzees could compare visible sets to nonvisible sets, and they were not distracted by perceptual illusions created through various presentation styles that were not relevant to the actual amount of juice dispensed.

"This performance demonstrated a similarity in the quantitative discrimination skills of chimpanzees for continuous quantities that matches that previously shown for discrete quantities."

Beran said of the chimps' preference for full measures: "The results support the position that chimpanzees are good mental accountants who judge various forms of quantities ... In some sense, this is a kind of folk understanding of the physics of liquids." ®

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