Continuous flash suppression

Chapter 4 endnote 45, from How Emotions are Made: The Secret Life of the Brain by Lisa Feldman Barrett.
Some context is:

In my lab, when we manipulate people’s affect without their knowing, it influences whether they experience a stranger as trustworthy, competent, attractive, or likable, and they even see the person’s face differently.

Hundreds of psychology experiments show how affect takes as its object whatever is in mind at the time. For example, affect influences your first impressions of people. If I manipulate your affect without your awareness, you’ll experience a new person as more or less trustworthy, reliable, competent, and even more or less attractive than you otherwise would. You’ll unknowingly use your change in affect as information about the world.

We demonstrate this phenomenon in our lab with a technique called continuous flash suppression that is commonly used to study consciousness. Using special equipment (a stereoscope), we present two different faces to a test subject simultaneously, one detectable by each eye. One face has a neutral expression and flashes on and off, alternating with geometric images. The other face, usually of a different sex, is displayed once for a very short time, around 200 milliseconds, at a very low contrast, and is either smiling, scowling, or neutral. In this special setup, the subject consciously sees only the flashing, neutral face (interspersed with geometric images). The static face is suppressed from awareness but is still detected and processed by the brain, and it influences the subject’s affect. When the unseen face is smiling, subjects feel more pleasant. They also experience the seen, neutral face as more trustworthy, more competent, more reliable, and/or more attractive. When the unseen face is scowling, subjects feel more unpleasant. They experience the neutral face as more negative, less trustworthy, and so on. Our newer experiments reveal that the unseen faces even influence judgments about whether someone is guilty of a crime, and how the test neutral face is literally seen (as more or less neutral). In short, people take the neutral face as the object of their change in affect; they experience their affect as a property of that face.

Behind the scenes, the brain detects and processes the static face with the same circuitry (the dorsal visual stream) it uses for predicting a ball’s location when playing baseball (chapter 4). So information about face is swept forward to limbic visceromotor regions. These regions initiate a new interoceptive prediction, and the subject’s affective feelings change, as does their perception of the neutral face that see (or that they are about to see, or that they just have seen). Affect is only sticky like this if the subject is unaware of what caused the affective change.