Fish can distinguish human faces they have amazing visual discrimination abilities
Fish have amazing visual discrimination abilities – they can distinguish human faces, even when presenting one familiar face with 44 others that they have never seen before, says a team of British and Australian scientists. The researchers were surprised, because fish lack a part of the brain that primates have, which they believed was necessary for facial recognition.
Dr. Cait Newport, Marie Curie Research Fellow in the Department of Zoology at Oxford University, and colleagues from the University of Queensland, explained in the journal Scientific Reports (citation below) that this is the first time any type of fish has demonstrated this ability.
Their experiments, which were carried out on a species of tropical fish – archerfish (Toxotes chatareus), also known as spinner fish or archer fish – showed that they could learn to recognise human faces with an incredibly high degree of accuracy.
Some examples of images of faces used in Experiment 1 (A) and Experiment 2 (B). Images shown are 3D morphs of several faces to protect the privacy of specific individuals. The Max-Planck Institute for Biological Cybernetics in Tübingen, Germany, provided all the images. (C) Illustration of the experimental setup. (Image: adapted from nature.com)
Facial recognition possible with smaller brain
This impressive feat requires sophisticated visual recognition capabilities, which scientists never knew fish had, that is, until now.
First author, Dr. Newport, said regarding this new ability discovered in fish:
“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. 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.”
“It has been hypothesised that this task is so difficult that it can only be accomplished by primates, which have a large and complex brain. The fact that the human brain has a specialised region used for recognising human faces suggests that there may be something special about faces themselves. To test this idea, we wanted to determine if another animal with a smaller and simpler brain, and with no evolutionary need to recognise human faces, was still able to do so.”
The archerfish catches its prey (which is out of the water) by squirting water bubbles at it. (Image: nature.com)
Fish do not have the sophisticated visual cortex that we and other primates have. However, the authors found that they were capable of discriminating one human face from forty-four new ones.
The scientists say their study provides evidence that fish, which lack a major part of the brain – the neocortex – have incredible visual discrimination abilities.
Fish squirted water on the familiar face
In this experiment, the archerfish – a species of fish from the monotypic family Toxotidae, known for their habit of preying on land-based insects and other small creatures by shooting them down with water droplets from their specialised mouths – were presented with two images of faces and trained to choose one of them by squirting water at it.
They were then presented with the familiar face and a series of new faces, and were easily able to correctly chose which face they had originally learned to recognise.
They were even able to do this accurately when some of the features, such as colour and head shape, were removed from the pictures.
In the first experiment, the archerfish reached an average peak performance of 81% accuracy, which improved to 86% in the second trial, even though facial features such as colour and brightness had been standardised in the second experiment.
Dr Newport commented:
“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.”
“Archerfish are a species of tropical freshwater fish that spit a jet of water from their mouth to knock down insects in branches above the water. We positioned a computer monitor that showed images of human faces above the aquariums and trained them to spit at a particular face. Once the fish had learned to recognise a face, we then showed them the same face, as well as a series of new ones.”
“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. Even when we did this with faces that were potentially more difficult because they were in black and white and the head shape was standardised, the fish were still capable of finding the face they were trained to recognise.”
In this video, you can see the archerfish squirting water at the face it recognises – every time.
This ability to distinguish between faces suggests that animals do not necessarily need to have a complicated brain to tell one human face from another. We may have special facial recognition brain structures so that we can process vast numbers of faces rapidly or under a wide range of viewing conditions.
Previous studies had shown that birds are able to distinguish human faces. However, they are known to possess neocortex-like structures, unlike fish.
The authors believe that fish are unlikely to have evolved the ability to tell one human face from another.
In an Abstract preceding the paper in the journal, the scientists wrote:
“Using a two-alternative forced-choice procedure, we show that archerfish (Toxotes chatareus) can learn to discriminate a large number of human face images (Experiment 1, 44 faces), even after controlling for colour, head-shape and brightness (Experiment 2, 18 faces).”
“This study not only demonstrates that archerfish have impressive pattern discrimination abilities, but also provides evidence that a vertebrate lacking a neocortex and without an evolutionary prerogative to discriminate human faces, can nonetheless do so to a high degree of accuracy.”
Citation: “Discrimination of human faces by archerfish (Toxotes chatareus),” Yarema Reshitnyk, Cait Newport, Guy Wallis & Ulrike E. Siebeck. Scientific Reports 6, Article number: 27523. 7 June, 2016. DOI: 10.1038/srep27523.
Video – Archer Fish Water Pistol
The archerfish makes a gun barrel by pressing its tongue against a groove in its mouth. It closes its gills to force out the water. It is accurate up to two metres.