Detecting differences in conscious contents using EEG complexity measures (Registered Report)

Ponce de Leon, S., Backer, K. C., Monti, M. M., & Yoshimi, J. (2025). Detecting differences in conscious contents using EEG complexity measures. In principle acceptance of Version 3 by Peer Community in Registered Reports. https://osf.io/kdsau

Measuring consciousness has been a longstanding problem. Even though behavioral responses are commonly used, converging evidence indicates that behavioral responsiveness and behavioral reports about consciousness dissociate from consciousness per se. Measures of complexity applied to brain activity, such as Lempel-Ziv complexity (LZc) and the perturbational complexity index (PCI), have been shown to discriminate between levels of consciousness, but less of this work has been done in the context of conscious content. To address many of the limitations of previous work, in this study we measure participants’ neurophysiological (EEG), subjective, and behavioral responses in states of normal wakefulness to visual and auditory stimuli that vary in granularity of subjective characteristics, such as meaningfulness. Two novel aspects of our study are that some of the visual and auditory stimuli are manipulated such that on most initial trials they are unrecognizable, but on some subsequent trials, they become recognizable. This allows us to measure changes in EEG complexity that correspond to differences in phenomenology alone while completely controlling for stimulus complexity. In addition, we are assessing if any of five dimensions of subjective ratings correlate with any differences in EEG complexity. This study advances our understanding of consciousness by clarifying the relationship between stimulus complexity and measures of brain complexity and phenomenology.

Figure 1. Overview of the visual tasks. Each trial will begin with black text that reads “Click + to proceed” displayed on a white background until the participant clicks the screen. After the click, the fixation cross will remain for 1 s to allow residual neural motor activity to dissipate, followed by the target image for 1 s (one of six categories/classes). After a random 33% of the trials (to control for task demands), participants will rate their experience from 1 to 5 according to five dimensions (consecutively): 1) diversity/richness; 2) unity/integratedness; 3) meaningfulness; 4) intelligibility/understandability; and 5) intensity/vividness. On the same 33% of the trials (to control for attention), participants will indicate which stimulus category/class they experienced (natural, blurred recognizable, blurred unrecognizable, or noisy). Each participant will complete 540 trials.

Funding:

• Initiative: Funding Consciousness Research with Registered Reports
• Organization: Templeton World Charity Foundation / Center for Open Science / ASSC
• Awarded: $31,932 USD