Mandelbrot cites his ability to "think in pictures" as fundamental to his process and insights.

He offers some interesting reflections and anecdotes on this subject in this interview describing his classes préparatoires aux grandes écoles. Apparently his teacher considered him a total wildcard case who would either flunk the exams or pass with flying colours, because of his habit of approaching everything through geometric intuition rather than symbolic manipulation.

https://www.webofstories.com/play/benoit.mandelbrot/6