With a neuroscience background, I can attest that this is yet again another example of hyperbole in pop psychology. However, it is interesting to note that PG said in one of his essays that the human mind constantly constructs a model unconsciously of the world around it.

That rang true to me because I've always noticed a phenomenon that occurs when I go to the mall. I get extremely tired (mentally) after just 2 hours. Why? My hypothesis is that I've taken in an unusually high amount of stimuli in those 2 hours by seeing, and possibly not even being aware of, thousands of items, prices, and faces.