Boy holding a fish
June 7, 2016

Fish can be trained to recognize faces, study finds

We know that our pet dogs and cats can recognize our faces, but our pet fish? That’s too far-fetched to believe, right? Not according to a team of scientists from the UK and Australia, who have discovered a species of tropical fish capable of distinguishing human faces!

The research, which was carried out by a team from the University of Oxford in England and the University of Queensland in Australia and published Tuesday in the journal Scientific Reports, found that archerfish were able to learn and recognize faces with a high degree of accuracy – a task which the authors noted requires highly-developed visual recognition capabilities.

This marks the first time that a species of fish has demonstrated such an ability, lead author Dr. Cait Newport, a research fellow in the Oxford Department of Zoology, and her colleagues said in a statement. Such abilities have been previously demonstrated in birds, but unlike fish, they have been proven to possess structures similar to the neocortex (the highly developed part of the brain that is associated with seeing and hearing in humans), the researchers added.

“Being able to distinguish between a large number of human faces is a surprisingly difficult task,” Dr. Newport said, “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.”

Study shows that complex brains aren’t necessary for facial recognition

In fact, she explained, the task is so difficult that some had hypothesized that only primates were capable of doing so, due to their large and complex brains. However, as previously mentioned, a previous study found that birds possessed similar capabilities, and Dr. Newport’s team wanted to see if other creatures with smaller, simpler brains could recognize human faces.

They discovered that fish, despite having no evolutionary need to do so and despite lacking any type of brain structure similar to the primate’s visual cortex, were able to recognize one familiar face out of a group of up to 44 never-before-seen ones. Their findings indicate that fish, despite their lack of a neocortex, nonetheless are capable of impressive feats of visual discrimination.

During their experiments, Dr. Newport and her colleagues presented archerfish with two images of human faces, and trained them to choose one using their ability to spit jets of water in order to knock down airborne prey. Next, the fish were presented with the familiar face and several that were unfamiliar, and were able to correctly pick the one that they had been trained to recognize, even when features such as head shape and color were removed from the selected pictures.

In the first experiment, the archerfish were tasked with picking the previously learned face from a group of 44 new ones, which they did with 81 percent accuracy. In the second, they were asked to choose in a scenario where facial features such as brightness and color had been standardized, and they proved to be 86 percent successful at this task.

“Fish have a simpler brain than humans and entirely lack the section of the brain that humans use for recognizing faces. Despite this, many fish demonstrate impressive visual behaviors and therefore make the perfect subjects to test whether simple brains can complete complicated tasks,” Dr. Newport said. “Once the fish had learned to recognize 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 recognize, 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 standardized, the fish were still capable of finding the face they were trained to recognize,” she added. “The fact that archerfish can learn this task suggests that complicated brains are not necessarily needed to recognize human faces.”

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