A couple million years ago (or a few thousand if you're a creationist Republican presidential candidate) humans began getting rewards for filling in the blanks, for adding two plus two, for drawing deductions. People who could do so survived, the others were eaten. Over time, the ability to "see" things before they were apparent became hardwired into our heads.
Here's what I mean.
Say it's two-million BC and you're out for a walk alone. Thirty feet ahead of you is a boulder. You notice that the bush around the boulder is tamped down and torn up. Something must be lurking behind that boulder. You turn on your calloused heels and avoid the lion lurking behind the rock.
You are rewarded (with life) for your ability to perceive.
Now, look at Kanizsa's Triangle, above. You see, of course, two triangles where there are none. This is another example of your brain doing work--of seeing things that aren't there. Of filling in the blanks.
Over the course of human history, humans have been "rewarded" for their ability to add up things that are barely perceptible. My lion example above is just one example.
We know ads work better when they give your brain the pleasure and reward of filling in the blanks. Yet, as Bob Hoffman pointed out in a comment on this blog the other day, so many clients want their advertising to "read" like a court case.
It's both sad and frustrating that the MBAs who approve our work and so often talk down to us because we wear blue jeans, know nothing of elementary neuroscience.
Our ads become prisoners of completionists. When they should, to be effective, allow the viewer's brain to do what it is wired to do.
By the way, if I ever get the nerve, funding or business to re-start my agency, GeorgeCo., I will begin every creative presentation with a brief discussion of Kanizsa's Triangle. It might even become my logo. After all, it looks also like a Jewish star.