Final answer:
The innovative vocal technique in scene iv of Act III of Berg's Wozzeck is Sprechgesang, a style between singing and speaking pioneered by Schoenberg and adopted by Berg for dramatic psychological expression.
Step-by-step explanation:
The innovative vocal technique heard in scene iv of Act III of Berg's Wozzeck pertains to the use of Sprechgesang, or 'speech-singing,' a vocal style that is between singing and speaking. Arnold Schoenberg, a contemporary of Alban Berg, was influential in developing this technique, which is characterized by a certain degree of atonality and a departure from traditional scales. Berg adopted this technique in his work to create a dramatic effect that serves the psychological exploration within the opera. This scene would have used Sprechgesang to convey the inner turmoil and fragmentation of the protagonist's mind.