In cognitive neuroscience, it has long been known that expectations influence what we perceive. A study just published in Advanced Science shows something different: expectations also affect how much we trust what we have decided, and they do so through a brain mechanism identified for the first time, the alpha oscillations of the right parietal cortex.
The study, titled “Prior Expectations Bias Confidence Judgments Through Parietal Alpha-Band Modulation”, was conducted by the Centre for Studies and Research in Cognitive Neuroscience of the Department of Psychology "Renzo Canestrari" (Cesena Campus), combining electroencephalography (EEG) and transcranial magnetic stimulation (TMS) on over 160 participants in two complementary experiments.
The research focused on metacognition, i.e. the ability to assess the correctness of one’s own decisions. In a series of perceptual tasks, before each trial the participants were given a probabilistic cue about the appearance of a stimulus; they were then asked to say whether they had seen it and how confident they felt in their response.
The result is clear: the probabilistic cues systematically modified confidence, increasing it when the response was consistent with the expectation and reducing it when it was in conflict, without altering the actual accuracy of the decisions. Expectations do not change how well we see, but how much we believe we see well.
In the second experiment, temporary inhibition of the right parietal cortex through TMS selectively attenuated precisely this effect, demonstrating the causal role of this area in "translating" expectations into subjective confidence.
"The confidence we have in our decision does not depend only on the quality of sensory information," explains Luca Tarasi, first author of the study. "The brain continuously integrates what it expects with what it perceives, and this integration shapes the judgement we make about ourselves."
"Metacognition is not just an update of our internal model on the basis of sensory evidence," adds Vincenzo Romei, last author and coordinator of the research. "Our work suggests that the ideal or expectation we have of the world also directly influences the interpretation of our own performance."
The effect described is not in itself a cognitive flaw: under conditions of uncertainty, anchoring confidence to expectations can help the brain maintain coherence and stability in monitoring its own choices. But an excessive reliance on this mechanism could contribute to significant distortions in clinical settings, from unwarranted confidence in one's own decisions to the rigidity of beliefs observed in psychiatric disorders in which the subjective assessment of reality is systematically altered.
The identification of a causal neural substrate such as parietal alpha oscillations also opens up the possibility of studying and modulating this mechanism with non-invasive brain stimulation techniques in the future.
The article, by Luca Tarasi, Anna Pasini, Domenico Romanazzi, Margherita Covelli and Vincenzo Romei, published in the journal Advanced Science, can be accessed at the following link
