EEG shows brain can simultaneous encode two speech streams

Researchers said EEG recordings show the human brain can simultaneously encode two competing speech streams during attention switches. The study published July 16 in PLOS Biology measured neural tracking in normal-hearing adults cued to switch attention between two talkers every 15 to 30 seconds amid background babble. Using temporal response functions, researchers found neural tracking of the new target stream emerged before disengaging from the previous target, revealing a transient simultaneous encoding. That transition was mirrored by a reduction in EEG alpha power. The team also isolated cortical activity reflecting lexical prediction mechanisms, comparing four context-accumulation strategies built with large language models. Findings suggest listeners may carry out a reset in lexical context after switching attention. The work was supported by the William Demant Fonden and Research Ireland.