The modulation of cognitive load on speech normalization: A neurophysiological perspective

Extrinsic normalization, wherein listeners utilize context cues to adapt to speech variability, is essential for maintaining perceptual constancy. In daily communication, distractions are ubiquitous, raising questions about the influence of cognitive load on this process, particularly at the cortical level. This study investigates how cognitive load modulates extrinsic normalization using electroencephalography (EEG). Native Cantonese speakers were asked to perceive Cantonese tones from multiple speakers with context cues in both single- and dual-task conditions. The secondary task did not hinder listeners' normalization process at the behavioral level. However, EEG data revealed significant modulations of extrinsic normalization under cognitive load. Extrinsic normalization elicited P2, N400, and LFN, suggesting that extrinsic normalization encompasses multiple perceptual adjustments at stages of phonological processing, lexical retrieval, and decision-making. Cognitive load influenced extrinsic normalization at all these stages, as evidenced by smaller P2, larger N400, and larger LFN, highlighting the active and controlled nature of this process.