Exploring the impact of social relevance on the cortical tracking of speech: viability and temporal response characterisation
Human speech is inherently social. Yet our understanding of the neural substrates underlying continuous speech perception relies largely on neural responses to monologues, leaving substantial uncertainty about how social interactions shape the neural encoding of speech. Here, we bridge this gap by studying how EEG responses to speech change when the input includes a social element. Specifically, we compared the neural encoding of synthesised undirected monologues, directed monologues, and dialogues in Experiment 1. In Experiment 2, we extended this by using podcasts, addressing the additional challenges of real speech dialogue, such as dysfluencies. Using temporal response function analyses, we show that the presence of a social component strengthens envelope tracking - despite identical acoustic properties - indicating heightened listener engagement. Neural responses to synthesised speech showed a strong correlation with those for real speech podcasts, with a stronger alignment emerging for more socially-relevant speech material. In addition, we demonstrate that robust neural indices of sound and lexical-level processing can be derived using real podcast recordings despite the presence of dysfluencies. Finally, we discuss the importance of dysfluency in social speech experiments, presenting a simulation quantifying the potential impact of dysfluency on lexical level analyses. Together, these findings advance our understanding of continuous speech neurophysiology by highlighting the impact of social elements in shaping auditory neural processing in a controlled manner and providing a framework for future investigation and analysis of social speech listening and speech interaction.