Perceptual ambiguity of the self - dynamics connect brain and behaviour

When the distinction between self and other is blurred, the self-other boundary is weakened, introducing perceptual ambiguity. The neural and behavioural mechanisms of resolving this ambiguity, and their interaction, are not known. To address this, we used a facial morphing task recorded in EEG, where participants' faces were morphed with the face of another in different proportions. Ambiguous images elicited different neural and behavioural dynamics than unambiguous images. Firstly, drift diffusion modelling of response behaviour revealed slower drift rates/evidence accumulation for ambiguous vs. unambiguous stimuli, which was accompanied by lower task-state neural measures of peak frequency sliding (PFS) in the theta band. Secondly, entropy of response times (RTs) and spectral entropy (SE) were higher for ambiguous vs. unambiguous faces, implying greater unpredictability and increased processing demand in both brain and behaviour. Notably, we identified neurobehavioural relationships for both dynamic measures. Resting-state theta PFS and ambiguous drift rates were significantly related, suggesting that stronger and faster internal information uptake during rest was related to better evidence accumulation for ambiguous faces. Moreover, SE on the neural level was related to behavioural entropy: smaller SE increase from rest to task was linked to lower RT entropy in the ambiguous condition, and thus better allocation of cognitive resources. Together, we demonstrate speed of information uptake and entropy/processing capacity are key in efficiently resolving self-other ambiguity, serving as the "common currency" (Northoff et al., 2020, 2025) of neural and behavioural levels of processing.