The narrative technique is stream-of-consciousness and it is used, in this novel, to create an astounding effect.
Each character given a chapter is represented in The Sound and the Fury by the workings of his or her mind. Dilsey and Quentin could not be more different as people, a fact which we discover very clearly when we read the chapters written from his and her point of view. Their tendencies, their challenges, their obsessions are all on display in the stream-of-conscious mode.
We can say then that this narrative technique is also a characterization technique.
The narrative technique used by Faulkner is known as stream of consciousness. This is when we learn each character's perspective directly, with no filter. We listen to the character's thoughts directly. Here is a descriptiion
Some readers find this narrative style freeing, because it's like being the character. Others just find it confusing.