We do several things at once
Nick Chater has just published a book The Mind is Flatwhich defends the same position as proposed here, i.e. that we do essentially one thing at a time. For example, for 1/3 of a second we do one thing, but then we can flip to another task, so it may look as if we are doing more than one thing at a time. He argues that examples like walking and chewing, though correct, should not distract from the essential simple message. Here is a section of the book ending in a reference to the 'walk and chew' case.
- Chater, N (2018) The Mind is Flat:The Illusion of Mental Depth and The Improvised Mind, Allen Lane, Random House, UK