"Unifying Textual and Visual: A Theoretical Account of the Visual Perception of Programming Languages" https://dl.acm.org/doi/abs/10.1145/2661136.2661138 direct pdf link: https://dl.acm.org/doi/pdf/10.1145/2661136.2661138
The paper offers a theoretical account based on the semiology of graphics from Bertin, using Lisp as an example (with very similar examples to Andrey's), but also other languages e.g. Befunge ;-)