Bertrand Russell’s Autobiogrpahy (1951) reports of mathematician and philosopher Alfred North Whitehead’s ability to focus:

[Whitehead’s] capacity for concentration on work was quite extraordinary. One hot summer’s day, when I was staying with him at Grantchester, our friend Crompton Davies arrived and I took him into the garden to say how-do-you-do to his host. Whitehead was sitting writing mathematics. Davies and I stood in front of him at a distance of no more than a yard and watched him covering page after page with symbols. He never saw us, and after a time we went away with a feeling of awe.