Neural Markers of Conscious and Non-conscious Speech Processing

Poster Session A - Saturday, April 13, 2024, 2:30 – 4:30 pm EDT, Sheraton Hall ABC

Gal Chen¹ (galrefa.chen@mail.huji.ac.il), Ran Hassin¹, Leon Deouell¹; ¹Hebrew University of Jerusalem

The processing of stimuli subjects are unaware of is highly debated, with studies focusing mostly on visual perception. As auditory inputs are profoundly different from visual, and rely on different processing streams, processes, and brain areas, examining audition is likely to bring novel insights and inform theories of consciousness. Using a new paradigm, we conducted two EEG experiments (total N=67; the second preregistered) in which participants performed a difficult visual task (1-back) while an ongoing stream of pseudowords was played. Single meaningful words, with lexical properties matched to the pseudowords, were embedded in this stream, and we tested awareness of word presence. In the second experiment, we added a manipulation for the relevance of word detection: before introducing the word detection task, participants performed only the visual task without informing or asking them about the presence of words. Our analyses revealed a late (>600 ms) frontal positivity evoked for undetected words vs pseudowords, reflecting non-conscious processing: the participants experienced nothing, yet the signal showed lexical processing. This response was significant for subjectively unaware trials in which participants were objectively incorrect regarding word category, weakening the possibility of unreported weak conscious processing. When word detection was irrelevant, the lexicality response disappeared. This result shows that words can be processed even though subjects are subjectively as well as objectively unaware of their presence. It also highlights that auditory unconscious processes are not mandatory, but goal-dependent: if we need to hear something relevant, we may process it even when it evades consciousness.

Topic Area: ATTENTION: Auditory