Absolute hearing threshold is a statistical construct, defined at 50% detection probability.

Evidence

An extreme example of a threshold is absolute threshold, i.e. the level of a pure tone necessary to be just audible. The threshold is not fixed for all time, but depends somewhat on the circumstances. Therefore, only a probability can be given that a certain stimulus level will lead to just-audible hearing sensations. This reasoning is illustrated in Fig. 1.7. Both the stimulus magnitude and the sensation magnitude increase in the vertical direction. However, below threshold the stimulus does not lead to a sensation. In the right panel of Fig.!. 7, the probability that a sensation is produced for different stimulus magnitudes is given. The conventional threshold is chosen to correspond to the probability 0.5. This means that in 50% of the trials, the “threshold” stimulus leads to a sensation, whereas in the other 50% of the trials, no sensation is produced. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 131

Categorization

• DEFINE: Defines absolute threshold as a probability-based concept (50% detection), not a fixed level.
• XREF: connects to: Auditory thresholds are measured by adaptive level bracketing with a 50 percent response criterion. — David Howard, Jamie Angus, coustics and Psychoacoustics, 2343