By guest blogger Sofia Deleniv
Back in the 1970s, the developmental psychologist Jean Piaget discovered that, if you ask young children to explain the mechanics of vision as they understand them, their answers tend to reveal the exact same misconception: that the eyes emit some sort of immaterial substance into the environment and capture the sights of objects much like a projector.
Although this belief declines with age, it is still surprisingly prevalent in adults. What’s more, so-called extramission theories of vision have a long-running history dating all the way back to antiquity. The Greek philosopher Empedocles was amongst the first to suggest in the 5th century BC that our ability to see must stem from an invisible fire beaming out of our eyes to interact with our surroundings. This view was subsequently endorsed by intellectual authorities like Ptolemy and Galen.
Now, a duo of researchers behind a recent publication in PNAS think they might have found an explanation for the intuitive appeal of extramission theories. According to their paper, this worldview might just be a reflection of the mechanisms that play out within our brains when we follow other people’s gazes and track where they pay attention. This is because, to carry out this process, our brains actually conjure illusory beams of motion emanating from other’s faces — a quirk of evolution with interesting consequences.
Scientists had already found signs that this was taking place. For instance, when people spend time looking at an image of someone gazing sideways at an object, they temporarily become slower at spotting subtle movement in that same direction. It is as if our brains treat the experience of seeing a pair of glancing eyes as an animated display of motion flowing towards the object of attention. This fatigues the brain region responsible for processing movement and renders it briefly “blind” to real motion along that same direction.
Shortly thereafter, an fMRI brain scanning study further deepened scientists’ suspicions. It showed that watching someone gazing at an object activated the motion-sensitive regions of our brains in a pattern that was remarkably similar to that triggered by the experience of viewing actual motion.
Tantalising as this evidence was, it was virtually impossible to conclude that this motion signal played any causal role in how we track people’s attention. Sceptical researchers suggested that the signal might simply reflect study participants imagining people reaching for the objects of their interest.
With this in mind, Arvid Guterstam and Michael Graziano — the Princeton University psychologists behind the recent PNAS publication — decided to set the causal record straight. They did this by testing whether meddling with the brain’s internal motion signal, using real (but subliminal) movement, could manipulate people’s perceptions of where someone was attending.
In their study, participants looked at a screen where two faces, set against a background of randomly moving black dots, gazed in the general direction of an object located at the center. They were asked to indicate which face seemed to be paying more attention to that item. But unbeknownst to them, these faces were actually mirror images, so participants unsurprisingly selected one or the other face with equal probability.
This changed when the researchers stealthily introduced a subtle signal in the background: a beam-shaped area emanating from the one of the faces, in which 30% of dots were made to drift coherently in the direction of the object. The manipulation was subtle enough that only seven out of over 650 participants were actually aware of it. And yet, it had a significant impact on how they attributed attention. On the trials where the subliminal beam of motion was flowing away from the left face, participants were 6% more likely to judge that face as paying more attention to the object — a significant deviation from their baseline indecisiveness.
Importantly, this motion-induced bias completely vanished when the dots moved in the opposite direction — i.e. from the object to the face. This suggests that our brains don’t fabricate motion signals for all interactions between objects in our surroundings. Rather, they reserve them for the social act of inferring the connection between someone’s gaze and the object of their attention. The byproduct of this, claim the study’s authors, is the inexplicable sensation that people’s eyes emit beams of immaterial substance. And even though this takes place outside the realm of our awareness, it might just be the driving force behind extramission theories’ historic and intuitive allure.
One almost cannot help but wonder whether this quirk of the brain also shapes how we intuitively think about mythical creatures. Indeed, aliens and robots with so-called “optic weaponry” have a propensity to pop up in works of science fiction, while medieval and classical-era tales are packed with beasts with killer glares (look no further than the basilisk, or the Gorgon Medusa, whose lethal gaze spurred the Greek hero Perseus to bring a reflective shield to his assassination attempt on the monster).
Of course, scientists will be hard pressed to prove that the historical and developmental appeal of extramission theories really is a reflection of the way our brains process gaze and attention. But these coincidences do raise interesting questions about the deep-seated role our fundamental neural mechanisms play in shaping our intuitions and imaginations — children and philosophers alike.
Post written by Sofia Deleniv for the BPS Research Digest. Sofia is a scientific writer whose work has appeared in magazines such as New Scientist and Discover Magazine. She holds a BA in Experimental Psychology and a PhD in Neuroscience from the University of Oxford, where she investigated how the brain processes sensations using a mix of electrophysiology and computer modelling. Ever enthusiastic about anything from genes and brains to animal behaviour, Sofia’s Twitter feed features the occasional update on her written work and other exciting bits of science.
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