The articulatory perceptions A are still within range for V2 but as they go farther up the signal for perceiving V1 gets stronger. The Sound perceptions S are still within range for V2 but as they go farther down the signal for perceiving V3 gets stronger.
The V1, V2, and V3 input functions are at the next level up. They provide input for perceiving words. That’s two levels up. Intending to perceive head, the subject controls both A and S perceptions to maximize the strength of the intended V2 signal at the phoneme level and to minimize the strengths of the V1 and V3 signals. The disturbance (not shown here) is what moves A and S apart from the intended V2 value of the sound S and the usual V2 value of the articulatory feel A which feels like pronouncing V2. If the experiment were to be prolonged, the reference A for articulation would become what it feels like to pronounce V2 and the resistance to the disturbance would be more complete. There the analogy to prismatic glasses might break down, because the glasses affect the entire visual field, and this equipment disturbs a limited part of the acoustic space of speech sounds.