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Scientists identify possible source of the ‘Uncanny Valley’ in the brain
Scientists have identified mechanisms in the human brain that could help explain the phenomenon of the ‘Uncanny Valley’ – the unsettling feeling we get from robots and virtual agents that are too human-like. They have also shown that some people respond more adversely to human-like agents than others.
Scientists identify possible source of the ‘Uncanny Valley’ in the brain. Photo: Andy Kelly/Unsplash
“Resembling the human shape or behaviour can be both an advantage and a drawback,” explains Professor Astrid Rosenthal-von der Pütten, Chair for Individual and Technology at RWTH Aachen University. “The likeability of an artificial agent increases the more human-like it becomes, but only up to a point: sometimes people seem not to like it when the robot or computer graphic becomes too human-like.”
This phenomenon was first described in 1978 by robotics professor Masahiro Mori, who coined an expression in Japanese that went on to be translated as the ‘Uncanny Valley’.
Neuroscientists and psychologists in the UK and Germany have identified mechanisms within the brain that they say help explain how this phenomenon occurs.
For a neuroscientist, the ‘Uncanny Valley’ is an interesting phenomenon. It implies a neural mechanism that first judges how close a given sensory input, such as the image of a robot, lies to the boundary of what we perceive as a human or non-human agent. This information would then be used by a separate valuation system to determine the agent’s likeability.
To investigate these mechanisms, the researchers studied brain patterns in 21 healthy individuals during two different tests using functional magnetic resonance imaging (fMRI), which measures changes in blood flow within the brain as a proxy for how active different regions are.
By measuring brain activity during tasks, the researchers were able to identify which brain regions were involved in creating the sense of the Uncanny Valley. They traced this back to brain circuits that are important in processing and evaluating social cues, such as facial expressions.
Some of the brain areas close to the visual cortex, which deciphers visual images, tracked how human-like the images were, by changing their activity the more human-like an artificial agent became – in a sense, creating a spectrum of ‘human-likeness’.
Along the midline of the frontal lobe, where the left and right brain hemispheres meet, there is a wall of neural tissue known as the medial prefrontal cortex.
In previous studies, the researchers have shown that this brain region contains a generic valuation system that judges all kinds of stimuli; for example, they showed previously that this brain area signals the reward value of pleasant high-fat milkshakes and also of social stimuli such as pleasant touch.
In the present study, two distinct parts of the medial prefrontal cortex were important for the Uncanny Valley. One part converted the human-likeness signal into a ‘human detection’ signal, with activity in this region over-emphasising the boundary between human and non-human stimuli – reacting most strongly to human agents and much less to artificial agents.
The second part, the ventromedial prefrontal cortex (VMPFC), integrated this signal with a likeability evaluation to produce a distinct activity pattern that closely matched the Uncanny Valley response.
The same brain areas were active when participants made decisions about whether to accept a gift from a robot by signalling the evaluations that guided participants’ choices. One further region – the amygdala, which is responsible for emotional responses – was particularly active when participants rejected gifts from the human-like, but not human, artificial agents.
The amygdala’s ‘rejection signal’ was strongest in participants who were more likely to refuse gifts from artificial agents. (University of Cambridge)
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