Double Dissociation in Alpha Wave Frequency and Amplitude Shape Visual Perception and Interpretation

Article: Is seeing believing? How neural oscillations influence our conscious experience
Source: University of Bologna (Italy)
Published: January 28, 2022 

Differences in alpha wave frequency (A) and amplitude (B) 
between TMS and sham for three study groups of varying IAF speeds 

Seeing is not necessarily believing. Neuroscientists in Italy provide the first causal evidence that despite their usual strong relationship, the perceptual accuracy of sensory observation and its subjective interpretation use separate neural mechanisms that can be manipulated independently of each other. Conducted with high density electroencephalogram (EEG) measuring the brain waves of 92 participants as they performed a visual detection task, the researchers show that the mechanisms behind what we see and what we think we see, originally thought to be overlapping processes, are actually dissociable. Specifically, the scientists found that the neural mechanisms behind conscious visual perception are due to oscillations in occipital alpha wave frequency (speed), which are responsible for processing objective sensory observation of external reality, with faster oscillations resulting in more accurate responses. First author of the study explains, "The results show that perception is a discrete rather than continuous process. Each alpha oscillations cycle represents a sampling cycle of sensory information, thus the faster the oscillations, the more information can be gathered, which in turn increases accuracy." For the subjective "internal representation" of the sensory event, which is related to the level of confidence in identifying what was seen, the scientists saw that these processes were related to occipital alpha wave amplitude, with a greater signal corresponding to a lower level of subjective confidence by the participants. Alpha wave amplitude is often associated with inhibitory processes, and their study shows that these inhibitory processes are related to subjective experience rather than objective accuracy.

TMS experiment results showing a causal relationship
between objective accuracy and alpha wave frequency (left)
and between metacognitive abilities and alpha wave amplitude (right)

In a second set of experiments, the researchers used transcranial magnetic stimulation (TMS) to directly and selectively control the frequency and amplitude of alpha oscillations to prove that these variations do influence the accuracy and confidence, respectively, in the perception of an image by a person. The researchers emphasize that visual perception is overall highly integrated, with subjective experience continuously being updated to match the sensory stimulus. Nonetheless, they report that the findings can inform the development of treatments for neurological and psychiatric disorders for those with altered cognitive experiences. Senior author of the study comments, "Altered cognitive experiences, such as confabulations or false memories, can be explained by the reduced integration between the subjective and objective components related to experience. Moreover, the dissociation between internal representation and external reality observed in the schizophrenia population might be caused by the non-communication between these two basic processes." 

My rating of this study: ⭐⭐

Di Gregorio F, Trajkovic J, Roperti C, et al. "Tuning alpha rhythms to shape conscious visual perception." Current Biology.  32(5):988-998. 27 January 2022. https://doi.org/10.1016/j.cub.2022.01.003