Absolute threshold of hearing

[3] It is approximately the quietest sound a young human with undamaged hearing can detect at 1 kHz.

The test presents the sound to the listener and manipulates the stimulus level in a predetermined pattern.

This means that sound may be present or absent in the single interval, and the listener has to say whether they thought the stimulus was there.

[4] Classical methods date back to the 19th century and were first described by Gustav Theodor Fechner in his work Elements of Psychophysics.

[12] The simple 1-down-1-up method consists of a series of descending and ascending trial runs and turning points (reversals).

After obtaining from six to eight reversals, the first one is discarded and the threshold is defined as the average of the midpoints of the remaining runs.

The threshold is thus tracked by the listeners, and calculated as the mean of the midpoints of the runs as recorded by the automat.

This is because 'top-down' influences mean that the subject expects to hear the sound and is, therefore, more motivated with higher levels of concentration.

The 'bottom-up' theory explains that unwanted external (from the environment) and internal (e.g., heartbeat) noise results in the subject only responding to the sound if the signal-to-noise ratio is above a certain point.

When the stimulus is presented to the listener one would expect that the sound would either be audible or inaudible, resulting in a 'doorstep' function.

In reality a grey area exists where the listener is uncertain as to whether they have actually heard the sound or not, so their responses are inconsistent, resulting in a psychometric function.

Sensitivity to sound improves as the signal duration increases up to about 200 to 300 ms, after that the threshold remains constant.