"...a challenging task: for example, watching letters appear on a computer screen every 1.6 seconds and documenting when one matched a letter that had appeared

"...a challenging task: for example, watching letters appear on a computer screen every 1.6 seconds and documenting when one matched a letter that had appeared three letters ago." It seems like they're conflating "stressful" and "thinking hard". IE, Is this "thinking hard" or is it "maintaining constant alertness"? I think things like staring at screen tax more than the brain as such. I spend most mornings working on math, programming and philosophy. This doesn't make me feel tired. Neither does playing the game of Go without a time limit. I assume all those tax the brain itself. But Zoom call will absolutely make me feel tired regardless of the subject. And "stress" could cause a build-up of glutamate or whatever in the brain also.