Undefined observation intervals prevent patients from anticipating signals and biasing thresholds low

Evidence

This paradigm uses an undefined observation interval, that is, the patient (or listener) does not know when the stimulus will be presented. In this way, the method prevents a patient from anticipating when a stimulus is presented, ensuring that the method will not yield a threshold lower than the true threshold. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 303