Visual-linguistic cues in manual communication: Neural and behavioral responses to Mouthings in sign-naïve perception

Gesture serves as a foundational modality for conveying event structure, providing critical visual information about transitivity and participant roles. Sign languages integrate manual (hand-based) and non-manual (face, torso, head) articulations to encode complex linguistic information. Among these, mouth movements provide phonological and lexical cues, but their role in sign-naïve individuals remains underexplored. This study investigates how sign-naïve individuals process non-manual markers (mouthings) in unfamiliar signed verbs, to explore how linguistic information is extracted from visual stimuli sharing properties with both gesture and sign language. Using EEG, we examined whether lip-reading functions as a linguistic cue or a general perceptual enhancement in non-signers viewing Austrian Sign Language (ÖGS) and non-ÖGS stimuli. Findings reveal distinct neural signatures for manual signs presented with and without congruent mouthings. An early posterior negativity followed by a late posterior positivity suggests that mouthings facilitate lexical access by providing phonological cues that activate stored lexical representations. Conversely, stimuli without mouthings elicited increased anterior activity, reflecting heightened cognitive control demands. Further, telic verbs, which inherently encode event endpoints, showed earlier and stronger facilitation from congruent mouthings compared to atelic verbs. These findings align with the Event Visibility Hypothesis and reinforce the role of visual cues in linguistic comprehension.