people construct synthetic perceptions inside their heads—and for this, I have coined the word umu- lus by combining stimulus and simulate. Thus in Chapter 3-8, I described how I used a simulus of Professor Challenger to disturb me enough to keep myself from falling asleep. To accomplish this, one might try to imagine all the details of such a scene; however, it might be enough merely to represent the high-level abstraction that there was a sneer on my rival's face—without constructing any other low-level details of that imagined simulus.