Plateau method in pure tone audiometry

　Audiometric configurations at a given frequency are classified into 12 patterns, and these patterns are grouped into four series.
　In a pattern [4-0], typical plateaus for both AC and BC in the left, poorer ear by AC are obtained. In the right ear , plateaus are not present.
The AC threshold measured without masking in the left ear (AL0) is the shadow hearing threshold, and the true AC threshold in the left ear (AL*) is AL0 plus ω (ω = AL*– AL0)). Then, the AC and BC plateau widths of the left ear (Lt APW, Lt BPW) are described below:

Lt APW = Rt AAgap + Lt SNC − ω. Lt BPW = Rt AAgap + IaB.

　Here, the difference between the AC thresholds measured without masking at some frequency is termed air and air gap (AA gap), and the Lt and Rt represent left and right, respectively:

Rt AA gap = AL0 − AR0. AR0 < AL0.

　The difference between the true BC thresholds (BL* and BR*) is termed a relative amount of sensorineural component of the left ear compared to the right ear (Lt SNC):

Lt SNC = BL* − BR*. BR* < BL*.

AA gaps serve as a clear indicator to predict the difficulty level of masking.

＜Abbreviation＞

AR0, BR0: the AC, BC threshold without masking in the right ear
AR*, BR* the true AC, BC threshold in the right ear
AL0, BL0: the AC, BC threshold without masking in the left ear
AL*, BL* the true AC, BC threshold in the left ear
IaA: the interaural attenuation for AC signals
IaB: the interaural attenuation for BC signals
ANmin: the minimum adequate masking noise level for AC
Nmax: the maximum adequate masking noise level

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Click the following website for more information.
Masking theory in pure tone audiometry – systematic lectures –
(https://izumo-yaegaki.jp).