Noise-induced high-frequency threshold shifts can make previously inaudible difference tones audible

Evidence

It should be pointed out, however, that noise-induced hearing loss, which produces mostly a threshold shift only at frequencies above about 1500 or 2000 Hz, produces conditions by which cubic or quadratic difference tones may become audible. Therefore, an additional masking noise should be added in the low frequency range in order to mask this possible difference tone which, if heard, would alter the shape of the tuning curve. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1891

Categorization

• QUESTION: Why does a high-frequency threshold shift make low-frequency difference tones audible? The mechanism connecting loss of masking at low frequencies to audibility of cubic/quadratic difference tones is worth chasing.
• DEFINE: Distinguishes cubic and quadratic difference tones - distortion products generated in the cochlea - as something that can contaminate tuning curve measurements.