While many people might have trouble picking out one tropical fish from another, the animals inside the tank looking out may not have the same problem. The keen eyesight and sharp brain of one tropical species has given them another talent, recognising human faces, according to a new study. A team of US and Australian researchers discovered the archerfish is able to distinguish between faces with a high degree of accuracy, the first time the trait has been seen in fish.
While the trick is second nature to many creatures living on dry land, it takes a surprising amount of brain processing, making the fishy feat all the more impressive. “Being able to distinguish between a large number of human faces is a surprisingly difficult task, mainly due to the fact that all human faces share the same basic features,” explained Dr Cait Newport, a researcher at the University of Oxford. “All faces have two eyes above a nose and mouth, therefore to tell people apart we must be able to identify subtle differences in their features. If you consider the similarities in appearance between some family members, this task can be very difficult indeed.”
Scientists believed that the mental task could only be carried out by primates – with some evidence to suggest others, such as dogs, also have the knack – and humans have a specialised region for facial recognition. But the team wanted to test if creatures with smaller, simpler brains and which had no need to recognise faces, could also carry out the task.
Most people will know the tropical archerfish for its spitting talent – when the animals feed by launching a jet of water from beneath the surface to knock insects of their perches above.
Working with researchers at the University of Queensland, the team found that fish were capable of discriminating one face from up to 44 new faces, despite lacking the sophisticated visual cortex of primates.
The research provides new evidence that fish have impressive visual discrimination abilities.
In the study, the tropical archerfish were shown two images of human faces on a monitor over their tank and were trained to choose one of them by spitting a jet of water at it. When the face was mixed in with new faces they were able to correctly choose the face they had initially learned, even when more obvious features, such as head shape and colour, were removed from the images.
On average, the fish were highly accurate, picking out the correct face from up to 44 faces 81 percent of the time, and 86 percent of the time when facial features such as brightness and colour were standardised.
Dr Newport said, “Fish have a simpler brain than humans and entirely lack the section of the brain that humans use for recognising faces. Despite this, many fish demonstrate impressive visual behaviours and therefore make the perfect subjects to test whether simple brains can complete complicated tasks.”
In all cases, the fish continued to spit at the face they had been trained to recognise, proving that they were capable of telling the two apart.
The researcher added, “The fact that archerfish can learn this task suggests that complicated brains are not necessarily needed to recognise human faces. Humans may have special facial recognition brain structures so that they can process a large number of faces very quickly or under a wide range of viewing conditions.”