Logan Trujillo

One of the most consistent event-related potential (ERP) correlates of phenomenal consciousness is the visual awareness negativity (VAN), a posterior negative shift in the ERP waveform within an approximately 200 – 300 ms post-stimulus time range for seen versus unseen visual stimuli [1]. This electrophysiological response likely originates from occipito-temporal cortical sources and may reflect the onset of recurrent cortical processing of visual information [1, 2]. However, there is still much unknown about the VAN, including its relationship to more general stimulus-evoked electroencephalographic (EEG) brain responses, which are partially indexed by ERPs. This presentation reports an exploratory study of this relationship that used a variant of an experimental design previously employed to investigate the VAN [2]. Seventy-two channels of scalp EEG were recorded while human participants (N = 27) performed a simple visual awareness task in which they rated the visibility of letter and number targets overlaid and surrounded by random visual noise. Six target visibility levels were created by altering the transparency of the visual noise overlaying the targets while keeping the noise of the surrounding background constant. The visual stimuli were randomly presented for 500 ms at central fixation followed by text instructing participants to rate target visibility on a slightly modified version of the 4-point Perceptual Awareness (PA) Scale (1= No Experience, 2 = Brief Glimpse, 3 = Almost Clear Experience, 4 = Clear Experience) [3]. We observed a statistically significant VAN ERP response to seen targets (Almost Clear Experience, Clear Experience) versus unseen targets (No Experience, Brief Glimpse). Wavelet-based time frequency analysis showed significantly greater alpha-band (8 – 12 Hz) phase-locked EEG power within the VAN time range over the posterior scalp for unseen versus seen targets. Moreover, alpha-band intertrial phase coherence (ITPC), a measure of the phase consistency of a stimulus-locked EEG signal across trials, was significantly greater for unseen versus seen targets in the VAN time range. Finally, an information-theoretic measure of the spatial complexity of alpha-band phase-locked EEG signals across the whole scalp and stimulus duration was greater for seen versus unseen targets. These preliminary findings suggest that the phenomenal consciousness-related neural processes underlying the VAN are more multifaceted than indicated by previous research. References: [1] Förster, J, Koivisto, M.,Revonsuo, A. (2020). ERP and MEG correlates of visual consciousness: The second decade. Consciousness and Cognition, 80, 102917. [2] Melloni, L., Schwiedrzik, C.M., Müller, N., Rodriguez, E., Singer, W. (2011). Expectations change the signature and timing of electrophysiological correlates of perceptual awareness. The Journal of Neuroscience, 31(4), 1386 – 1396. [3] Overgaard, M., Rote, J., Mouridsen, K., Ramsøy, T.Z. (2006). Is conscious perception gradual or dichotomous? A comparison of report methodologies during a visual task. Consciousness and Cognition, 15, 700 –708.

Dr. Logan Trujillo is an associate professor in the Department of Psychology at Texas State University. He is also currently an Associate Editor for the Journal of Consciousness Studies. Dr. Trujillo holds degrees in mathematics (BS), physics (MS), and psychology (BS, MA, PhD) from the University of Arizona, where as a student he was an affiliate of The Center for Consciousness Studies. Dr. Trujillo’s research provides basic and applied insight into the physical, neural, and psychological mechanisms underlying human mental information processes such as sensation and perception, attention, cognitive control, and consciousness. He achieves this through the measurement, quantitative analysis, and computational modeling of human behavior, subjective reports, and brain activity.