Masking occurs before, during, and after a masker is present.

Evidence

Three different temporal regions of masking relative to the presentation of the masker stimulus can be differentiated. Premasking takes place during that period of time before the masker is switched on. In this period, negative values of i1t apply. … After the end of the masker, post-stimulus masking, normally called postmasking, occurs. During the time scale given by positive delay time, td, the masker is not physically existent; nevertheless, it still produces masking. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 485

Categorization

• DEFINE: Defines the three temporal masking regions: premasking, simultaneous masking, and postmasking, along with the key term sensation level.