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Study reveals links between bodily rhythms and visual perception
A study funded by the SNSF highlights previously unknown links between the body and the brain. The findings of this research carried out at the University of Fribourg show how our bodily rhythms affect our visual perception.
Taking a deep breath to get a clearer picture is perhaps more effective than you might think. Breathing has a physiological impact on the perception of visual stimuli. This is what emerges from the work of Juliane Britz, a psychologist and neuroscientist at the University of Fribourg. She has set up an experiment demonstrating that cardiac and respiratory rhythms have an impact on how we become conscious of a visual stimulus. The results of this study, funded by the Swiss National Science Foundation (SNSF), have just been published in the journal PNAS.
Seeing an image without realizing it
For this study, volunteers observed a screen on which grey squares appeared briefly, either cross-hatched diagonally in one direction or the other. After each visual stimulus, the subjects were asked two questions: Had they seen the patterns or not, and what was their orientation? The contrast of the crosshatching was calibrated so that participants consciously saw it 50% of the time. However, even though it was only consciously perceived one time out of two, the orientation indicated was correct 85% of the time. This means that by following their intuition – even without knowing where it came from – the subjects were right more often than if they had answered randomly. It therefore seems that the volunteers sometimes processed the patterns without realizing it.
Throughout the experiment, electrodes were used to measure the electrical activity in the participants’ brains (electroencephalogram, EEG) and hearts (electrocardiogram, ECG). Their breathing was also tracked using a belt that measured the abdominal volume. Comparing the brain’s electrical signals between cases where the subjects had seen the crosshatching or not allowed the psychologist to identify “neuronal markers of consciousness”.
She and her team then compared these neural markers according to cardiac phase. The analysis showed that if the image was displayed while the heart was relaxed, the markers of consciousness appeared around 150 milliseconds earlier than if the image was displayed while the heart was contracting. Breathing has a similar impact on visual perception, with the same delay when the image appears during exhalation rather than inhalation.