Final answer:
A transition is the shift you hear when the central theme drops out in music.
Step-by-step explanation:
The shift you hear when the central theme drops out is called a transition. This is a musical signpost language that allows the listener to know that the author is moving from one key idea to another. It can be recognized by a change in melody, harmony, or rhythm. In the example given, when the central theme of the music drops out and the dissonance of the chords increases, this creates a shift that indicates a change in the scene or mood of the film.