Studies have shown that both human and non-human primate infants preferentially look at faces. But is this preference for faces hardwired? That is the question at the heart of a study published this week in Nature Neuroscience.
Led by Dr Margaret Livingstone, the researchers from Harvard Medical School, reared three macaques in the absence of seeing any faces – primate or otherwise. The monkeys were reared by humans wearing gloves and welder’s masks. They were provided with fur-covered surrogates and soft-toys so that their environment was otherwise stimulating. They were kept in a curtained off room which was part of a larger monkey enclosure so that the face-deprived macaques could still smell and hear other monkeys.
After a few months, the face-deprived monkeys were shown a series of images while their brains were monitored using functional MRI scanners. These monkeys were compared to ones who had been raised normally. The monkeys wore a foam-padded helmet that delivered them juice as a reward for looking straight at the screen. After the experiment, the monkeys were introduced to normal life. Livingstone notes that while the monkeys “still don’t look at faces much… they seemed pretty social to us”.
Livingstone adds that they were able to build upon the lessons learned from the psychologist Harry Harlow’s experiments in the 1950s, which infamously deprived infant monkeys from their mothers as soon as they were born. Today’s researchers worked to “prevent them [the monkeys] from being depressed or withdrawn”, and that potential problems they had forseen “fortunately, did not emerge”.
The scans showed that the face-deprived monkeys did not possess a “face patch” in their inferior temporal cortex, the part of the brain associated with visual recognition. In other words, they didn’t know what a face looked like, and consequently could not recognise it.
Face selectivity, the researchers concluded, had to be learned. The researchers also found that the “scene patches” for all other objects seemed to have developed normally. Moreover, the actual wiring on the neurons in the visual system also appeared normal.
By contrast, normally-raised monkeys appeared to look disproportionally at faces, even before their “face patches” had developed.
The researchers theorised that our preference for faces at a very young age could be due to “low-level perceptual biases” and “reinforcement learning”.
In layman’s terms, you may not be born with the ability to recognise faces, but parts of our visual system are primed to become face selective with experience. This is because we are innately biased towards curves and things which are animated.
Not only that, but when you look at someone’s face, they tend to react. The more the monkeys look at other faces, the more their behaviour is reinforced by the faces they are looking, and so they further develop the skill of recognising faces. Livingstone points out that “the brain is a statistical learning machine and it wires itself up to deal with whatever it is presented with.” Seeing makes you better at seeing.
So rather than monkey see, monkey do, it should be monkey see… oh you get the joke.