Hearing aids restore loudness sensitivity but cannot restore damaged frequency selectivity.

Evidence

740 Hz. For the high frequencies of 4 kHz, the hearing loss is even greater, the form of the tuning curve is again very flat towards low frequencies, and the slope towards high frequencies has an angle on these coordinates that is only one quarter that of normal hearing subjects. This means that the frequency selectivity of patients in this group is distinctly worse. Under such conditions, an amplifying hearing aid may bring back the sensitivity as such, but cannot restore the impaired frequency selectivity. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1890

For the high frequencies of 4 kHz, the hearing loss is even greater, the form of the tuning curve is again very flat towards low frequencies, and the slope towards high frequencies has an angle on these coordinates that is only one quarter that of normal hearing subjects. This means that the frequency selectivity of patients in this group is distinctly worse. Under such conditions, an amplifying hearing aid may bring back the sensitivity as such, but cannot restore the impaired frequency selectivity. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1890

Categorization

• XREF: Connects to the broader theme of hearing loss and the limits of corrective devices — relevant to the reader’s psychoacoustics model-building as a boundary condition on what amplification alone can fix.
• corroborated: 2 independent passages support this claim — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1890