Multichannel Multitasking
Multichannel multitasking is Nir Eyal's label, from Indistractable in 2019, for a carve-out from the general finding that multitasking is costly: two tasks competing for the same channel interfere, while two tasks using different channels can sometimes run together. The underlying science is Christopher Wickens's multiple resource theory, and the carve-out is real but narrower than the label suggests. Cross-modal pairs still compete for central control, so the right test is not whether the senses differ but whether one of the tasks is automatic.
What it is
Eyal concedes the standard finding before making his exception, which is what makes the exception credible. Two podcasts, one in each ear, is impossible. An audiobook while walking is not.
The mechanism he invokes is sensory: different channels, less collision. The better statement of it is Wickens's multiple resource theory, published in Theoretical Issues in Ergonomics Science in 2002, which holds that tasks drawing on different modalities interfere less than tasks sharing one. That part is well supported.
The limit is where the popular version goes wrong. Adam Gazzaley and Larry Rosen concede the same thing Eyal does, that genuinely parallel processing happens and automated actions can run alongside a task at no cost, and then draw the boundary more sharply: the competition is not for a sensory channel, it is for cognitive control. Two tasks that both need the prefrontal cortex compete even when they arrive through different senses, which is why the brain switches networks rather than running both.