It is from Crash Course World History. It is at 6 minute and 21 second. Here is the context:
Since looking at the landscape was no longer the same experience, and according to the medical journal The Lancet, "The rapidity and variety of the impressions necessarily fatigue both the eye and the brain", many people turned to reading books on railroads.
I have checked all the meanings of the word impression and I am still struggling to understand what it means there.