The chapter describes how Feynman came across how his colleague visualizes a task. IIRC Feynman does it visually (imagines something visual in his mind) and thus can do voice related activities while he is thinking, but his colleague does it by visualizing sound (he thinks tick-tock sounds in his mind), so can do visual tasks while he is thinking.
Really fascinating how a human mind works.
Also reminds me of the quote by Einstein, something about judging the ability of a fish to climb a tree.
Everyone has a unique and effective way to navigate the world intellectually.