Leonard Mlodinow wrote in Subliminal that in 2005, Caltech's Christof Koch came up with a way to study unconscious vision by manipulating a subject's binocular rivalry to create an artificial blind spot.
Using Koch's discovery, a group of scientists exposed each subjects right eye "to a colorful and rapidly changing mosaic-like image and the subject's left eye to a static photograph that pictured an object." (i.e., the image on the right changed, and the image on the left didn't change.)
The object was placed near the right or left edge of the photograph. Because they couldn't consciously see the (static) image, the subjects had to guess where the object was located.
When an unprovocative static image was used, the subject's answers were expectedly correct about 50% of the time, but when a provocative static image of a nude woman was used, the men did "significantly" better at guessing which side the (nude) image was on - despite the fact that the men were "clueless" and couldn't consciously see the pornography.
Mlodinow wrote "We don't consciously perceive everything that registers in our brain, so our unconscious mind may notice things that our conscious mind doesn't"
And that "[d]eep concentration causes the energy consumption in your brain to go up about 1 percent. No matter what you are doing with your conscious mind, it is your unconscious that dominates your mental activity - and therefore uses up most of the energy consumed by the brain"
And I would assert, using this as evidence, that writer's block is a (Hollywood) myth. If one thinks long enough, material will move from the unconscious to the conscious.