Which part of the brain “accumulates evidence” for what we see, how this process depends on our reactions, and how it is influenced by our confidence — these are the key questions addressed by an international research project involving the Milan Brázdil Research Group from the Brno Centre for Neuroscience at Masaryk University. In their study, the scientists built on the very first research of its kind in the world from 2001, in which the Brno team used analysis of EEG signals recorded by special electrodes placed directly in the human brain to study human consciousness. They have now described the role played by the visual cortex in our perception and demonstrated that its foundation is deeply visual in nature. The study was published in the journal Nature Communications.
The visual cortex processes everything we see, from colors and shapes to written text and highly complex images. It is divided into two main parts — the ventral stream (which determines what we see) and the dorsal stream (which determines movement and spatial location, i.e., where we see it). Damage to this area can result in a condition in which a patient can see but is unable to name the objects they perceive. Until now, it was assumed that the ventral stream functioned merely as a “passive detector” that registers images and sends them to higher visual centers. However, the scientists have shown that at this level the brain not only “accumulates evidence,” but that active signal analysis already takes place in the ventral visual cortex, determining whether the signal is strong enough to give rise to the perception that we are truly seeing something.
“Our data show that the active decision-making center that gives us the feeling that we see something is already the ventral visual cortex,” comments Associate Professor Robert Roman from the First Department of Neurology at St. Anne’s University Hospital and the Faculty of Medicine, Masaryk University. The scientists worked with patients with epilepsy who had electrodes implanted directly into their brains as part of their treatment. The patients were shown faint images of faces obscured by visual noise and were asked to press a button as soon as they recognized a face. Their brain activity was monitored during the task. The results showed that “evidence accumulation” appeared more quickly during faster reactions; however, a similar pattern was also activated when participants believed they saw a face that was not actually present in the image.
Previous research had suggested that these processes occur primarily in the frontal or so-called parietal regions of the brain, where decision-making and response planning (such as pressing a button) take place. The finding that the signal originates already in the visual cortex and functions even without any task instruction demonstrates that it is tied to vision itself rather than to the response. This represents a valuable contribution to studies on the neural basis of consciousness, which often measure only attention or motor preparation rather than pure perception. The study thus highlights the visual foundation of conscious perception. “Such signals can potentially be detected non-invasively using EEG or MEG, and these markers of conscious perception could in the future serve as new tools for assessing the condition of patients for whom verbal responses cannot be relied upon, for example those who are unconscious. Results based on real clinical data also open the way to better mapping of brain networks during epilepsy surgery,” concludes Professor Milan Brázdil, Head of the First Department of Neurology at St. Anne’s University Hospital and the Faculty of Medicine, Masaryk University.
