Zero? Is that even possible?
When using a laptop, it's impossible to look at the display without being able to also look at the keyboard (and touchbar) by just moving your _eyes_. You don't have to move your head.
I think your assumption is not reasonable at all.
I don't look at my keyboard when typing so other than the slight realization that it is there on a laptop I never look at it (but yes it would technically be in my field of vision in this case but that misses the point). However on a desktop setup / docked laptop the keyboard isn't anywhere near where I could see it without significantly moving my head down.
Regardless discussing field of vision is more of a red herring in this debate; it's really about the eye movement and context switching. I should have chosen different wording.
> When using a laptop, it's impossible to look at the display without being able to also look at the keyboard (and touchbar) by just moving your _eyes_. You don't have to move your head.
I think you confuse the physical act of moving ones head to be more disruptive than moving one's eyes. It's actually about the same when you're talking UX assuming the head is moving to change the field of vision. This is something you keep track of and many times head movement will be removed or ignored from testing data when you're tracking where the user is looking because you can move your head and still keep your eyes in one place.
I hope you understand that you move your eyes when you look at different things on your display. The touchbar is just another display that is only slightly lower than the lowest part of your display. You don't need to move your head to see that, only your eyes. The same eyes you move when you look at different things on the main display.
But of course. That was a huge part of my point. Moving your eyes off the display is a _big move_. It's not a typical UX pattern. These things are very well tracked in user testing with eye tracking. The idea is to incrementally move their eyes and never require large movements else you end up having UX issues.
Judging from the downvotes I'm guessing many haven't looked into or used eye tracking during user testing. It's quite interesting, you should check it out!