Brain tracks dual speech streams when switching attention

The brain handles auditory attention shifts less like a hard toggle switch and more like a crossfade, temporarily running parallel speech-tracking systems and resetting its semantic context window to adapt.

• –**Parallel Encoding:** Cortical representation of a new speaker starts before the brain disengages from the previous one, showing a brief dual-tracking mechanism.
• –**Alpha Power Drop:** Transition phases are marked by decreased alpha band power, signaling increased cognitive load and attentional control.
• –**Lexical Reset:** LLM-based modeling suggests the brain resets lexical expectations after a switch rather than blending contexts.
• –**Assistive Tech Value:** Insights into how the cortex filters speech can guide the design of future neuro-steered hearing aids and auditory interfaces.