HOW DO WE BECOME AWARE OF WHAT (WE THINK) WE SEE?
Oscillatory mechanisms of conscious perception
Jelena Trajkovic1, Francesco Di Gregorio2, Paolo Di Luzio1, Eleonora Mercantoni1, Alessio Avenanti1, Gregor Thut3, Vincenzo Romei1,4
1 Centro studi e ricerche in Neuroscienze Cognitive, Dipartimento di Psicologia, Alma Mater Studiorum – Università di Bologna, Campus di Cesena, 47521 Cesena, Italy;
2 Azienda Unità Sanitaria Locale, UOC Medicina riabilitativa e neuroriabilitazione, 40139, Bologna, Italy;
3Institute of Neuroscience & Psychology, University of Glasgow, UK
4 IRCCS Fondazione Santa Lucia, 00179 Roma, Italy.
Alpha-oscillations have an active role in sensory processing and conscious perception. Specifically, recent reports suggest that pre-stimulus alpha-amplitude reflects perceptual bias, not accuracy, during visual decision-making. What are then oscillatory correlates of perceptual accuracy? Individual alpha-frequency (IAF) seems to have a relevant role in temporal sampling, such that faster alpha-oscillations lead to higher accumulation of sensory evidence over time, resulting in more accurate perceptual experience. Importantly, we hypothesize here that this higher temporal resolution for visual sampling can successfully translate into higher spatial mapping, by allocating more resources in space. In the present work, we used a visual detection task with spatially lateralized stimuli, firstly to directly test the hypothesis that IAF and alpha-amplitude selectively account for objective accuracy and subjective confidence, respectively. Moreover, in a second experiment, we independently targeted pre-stimulus IAF and amplitude by rhythmic Transcranial Magnetic Stimulation protocols, thus testing how changes in these two parameters of alpha lead to distinct behavioral changes. We found that accuracy is best predicted by modulations of the pre-stimulus IAF. Specifically, induced faster vs. slower alpha-TMS oscillations directly lead to higher vs. lower task accuracy, not confidence. Finally, we causally substantiated the emerging view that alpha-amplitude modulations selectively reflect the degree of subjective confidence, with IAF-tuned TMS-pulses aimed at enhancing alpha-amplitude leading to lower confidence ratings. Here, we offer a first causal evidence of a functional dissociation between distinct parameters of alpha-activity in shaping conscious perception: while IAF accounts for the accuracy of our perceptual experience, alpha-amplitude shapes its’ subjective interpretation.