Advancements in the study of neuroscience have shown that there are several kinds of circumstances where what we think we’ve seen isn’t actually what passed before our eyes, and a new study from the Netherlands, utilizing an extremely intimate view of human neurology, has shown that this is especially true for routine actions.
When we engage in social interactions, like shaking hands or having a conversation, our observation of other people’s actions is crucial, but if the picture of action becomes too familiar, reports from a human brain with electrodes implanted directly in the cranium showed that we begin to see how we would perform the action, or how the action ought to be performed, rather than what’s actually happening.
According to one member of the research team, this might lead to certain details going completely unnoticed by a viewer, and reinforces that our brains are choosy about what information they decide to perceive.
“While things unfold approximately how you expect them, the information that your brain makes you perceive is no longer information that came in from the eyes, but information that was self-generated by your own motor system,” Christian Keysers, a senior author of the study and director of the social brain lab at the Netherlands Institute for Neuroscience, told WaL.
Keysers and his colleagues, together with the Jichi Medical University in Japan, received an extremely rare opportunity to run this trial after they were allowed to measure brain activity directly from the brains of epilepsy patients who participated in intracranial EEG-research for medical purposes. Such an examination involves measuring the brain’s electrical activity using electrodes that are not on the skull, but under it.
Clinically, it’s used as a final step for medication-resistant epilepsy patients, as it can determine the exact source of epilepsy. But while the medical team waits for epileptic seizures to occur, these patients have a period in which they have to stay in their hospital bed and have nothing to do but wait. Researchers used this period as an opportunity to peek into the workings of the brain with unprecedented temporal and spatial accuracy.
The wheels driving the car
It was previously thought, based on observations of the brains of humans and monkeys watching an action in isolation in a lab, that visual perception occurred first and that the parietal cortex and premotor cortex acted after. But being that a single action, such as picking up a knife, when viewed in an environment with a bread roll, butter, and a plate, will also infer the conditions for the end goal of snack making, Keyser et al. wanted to see how the brain reacted differently.
During the experiment, participants watched a video in which someone performed various daily actions, such as preparing breakfast or folding a shirt. During that time, their electrical brain activity could be measured through the implanted electrodes across the brain regions involved in action observation to examine how they talk to each other.
Two different conditions were tested resulting in differing brain activity while watching. In one, the video was shown in the way we would normally see the action unfold every day. Someone picks up a bread roll, then a knife, then cuts open the roll, then scoops some butter, etc.; in the other, these individual acts were re-shuffled into a random order. People saw the exact same actions in the two conditions, but only in the natural order can their brain utilize its knowledge of how it would butter a bread roll to predict what action comes next.
Using sophisticated analyses in collaboration with Pascal Fries of the Ernst Strüngmann Institute (ESI) in Germany, what the team could reveal is that when participants viewed the reshuffled, unpredictable sequence, the brain indeed had an information flow going from visual brain regions, thought to describe what the eye is seeing, to parietal and premotor regions that control our own actions. But when participants could view the natural sequences, the activity changed dramatically.
“Now, information was actually flowing from the premotor regions, that know how we prepare breakfast ourselves, down to the parietal cortex, and suppressed activity in the visual cortex,” explains Valeria Gazzola, a co-author on the study. “It is as if they stopped to see with their eyes, and started to see what they would have done themselves”.
This isn’t the only documented case of the brain ignoring information coming from the visual cortex while determining perception, as strange as that sounds. In a recent study conducted at the Max Planck Institute for Biological Cybernetics in Germany, Dr. Abhilash Dwarakanath and an international team of collaborators found that brain wave patterns can predict when the brain switches the root of perception from the visual cortex to the prefrontal cortex, and from eyeball to eyeball.
In a summary of their paper, Dwarakanath explains that by observing beta brain waves, which oscillate between groups of neurons at about 20-40 hertz, one can predict with a high degree of correctness when the prefrontal cortex, a part of the brain associated with complex decision making and problem-solving, will switch perception from each eye or from the visual cortex to other regions. The paper explains the phenomenon of binocular rivalry prevents the human brain from observing two separate things when viewed in isolation, as can be tested by having participants look into arrays of mirrors in which two separate objects, say an apple and a rose, are presented to each eye.
Similarly, Keyser and Gazzola’s experiment demonstrated that our brain does not simply react to what comes in through our senses. Instead, we have a predictive brain, that permanently predicts what comes next. The expected sensory input is then suppressed, and we end up seeing the world from the inside out, rather than from the outside in. If, however, what we see violates our expectations, the expectation-driven suppression fails, and we become aware of what we actually see rather than what we expect to see.
“Would you miss details?” asks Keysers hypothetically, when asked whether this predictive cognition could actually obscure what was happening. “This is not something that we deliberately examined in this particular experiment, but based on the overall state of the psychological literature, one can venture a pretty safe bet along the following lines: if you put your full attention onto the details of what you see, and the discrepancy is significant, your system would detect the prediction error, and you would become aware of the unexpected action”.
“If on the other hand, your attention is elsewhere or the deviation is subtle, you would not notice,” he adds. “This is what magicians use when they trick you: make one large salient action that captures attention and matches an observer’s expectations, and people will never notice the other hand that performs the trick”. WaL