Speech Streams
A recent study looking at the human brain’s capacity to focus on spoken language streams and shift attention from one stream to another found that we can process two conversations at once, but we generally only do so for a second or two at a time.
The researchers used EEG recordings from adults with normal levels of hearing and had them listen to two competing speech streams simultaneously. They were tasked with switching their attention between the two competing speech streams every 15 to 30 seconds, and their neural tracking (what their brains were focused on at any given moment) was assessed using Temporal Response Functions, which are mathematical models that help quantify how the brain processes audio inputs, including, in this case, when the brain has switched from processing one input to another.
What they found is that there’s a momentary handoff mode during which the brain is still listening to the conversational stream it has been actively tracking, but also starts listening to the stream it’s about to switch over to, creating a sort of informational buffer that contains information from the new stream while still processing information from the current stream.
There’s a fair amount of variability between people, in terms of their dual-stream buffer capacity, and this might shape a person’s natural propensity toward being able to navigate complex social situations and noisy environments, as their brains may be more or less capable of quickly switching between streams of info-laden sound.
This also gestures at a possible source of the exhaustion some older and hard of hearing people feel in noisy situations: when this buffering system is strained, we’re forced to expend more effort (consume more energy) to distinguish one audio stream from another. So if our hearing is anything but optimal, there’s a chance this buffer system won’t work at full capacity, and every complex conversation or noisy environment will require more concentrated focus (and thus, require more effort) to navigate.