The Quality of Our Perception of the World Depends on the Speed of Alpha Brainwaves

When we look at the world around us, we have the impression of perceiving it in a smooth, continuous way. In reality, our brain could function like a very high-definition camera, capturing rhythmic snapshots of reality and reassembling them into a coherent experience.

These are the findings of a new study published in Nature Communications and conducted by Professor Vincenzo Romei and Researcher Luca Tarasi, both working at the Department of Psychology "Renzo Canestrari" of the University of Bologna. The study centres on alpha brainwaves, one of the main electrical rhythms observable in humans.

“Our study shows that the speed of alpha oscillations – a brain rhythm that oscillates between seven and 13 times per second – is linked to the accuracy with which we perceive the world: the faster the alpha rhythm, the greater the perceptual sensitivity,” explains Vincenzo Romei. “We also know that alpha frequency tends to slow down with age and is altered in neuropsychiatric conditions such as schizophrenia: a slowing of the alpha rhythm could therefore translate into less accurate sampling of reality, contributing to distorted representations of the environment”.

The role of alpha brainwaves has emerged in recent years as an important element in the process of dividing sensory processing into distinct units. In particular, each brain oscillation alternates between moments that are more favourable and moments that are less favourable for perception.

The process is similar to a door onto the outside world that opens and closes rapidly. If the oscillation rhythm is slow, a stimulus can more easily be received at an “unfavourable” moment, and therefore it will produce a less well-defined perception of reality. If, on the other hand, the rhythm is faster, the stimulus is more likely to be caught at the right phase, resulting in a sharper perception of reality.

“It’s not a question of seeing for longer: it’s a question of having more opportunities, at the same time, to latch on to the optimal moment to perceive correctly,” explains Luca Tarasi. “The definition of what we see depends, at least in part, on the speed at which our brain takes its internal snapshots of the outside world.”

To test the phenomenon, the researchers carried out an experiment with 125 participants, one of the largest samples ever used in this field. Through electroencephalography (EEG), they measured alpha frequency moment by moment before providing a very brief visual stimulus (59 milliseconds). The results were surprising: when the alpha rhythm was faster in the moments immediately preceding the stimulus, participants were more accurate in identifying what they had seen.

This greater accuracy did not depend on greater confidence in the response. Rather, the computational models used showed that alpha frequency increased the likelihood of correctly identifying whether or not the stimulus was present. In other words, it increased the quality of sensory processing.

“These are not just general differences between people, but moment-to-moment fluctuations: even within the same individual, when the frequency of alpha waves speeds up, perceptual sensitivity increases,” says Romei. “These results suggest that the brain operates like a sampling machine: the faster it oscillates in the alpha rhythm, the greater the sampling resolution, and therefore the higher the likelihood of accurately capturing what is happening in the outside world.”

In addition to providing solid evidence for the idea that perception is not continuous but rhythmic, the study could also pave the way for new treatments for those who live with distorted representations of the environment due to old age or neuropsychiatric conditions such as schizophrenia. The researchers suggest that selectively modulating alpha frequency through non-invasive neurostimulation or with neurosensory training protocols could prove to be an effective strategy for improving the fidelity of perception.

The study was published in Nature Communications with the title “Alpha frequency shapes perceptual sensitivity by modulating optimal phase likelihood”. The authors are Vincenzo Romei and Luca Trasi, a full professor and a research fellow at the Department of Psychology "Renzo Canestrari" of the University of Bologna.