Impaired frequency selectivity directly causes poor speech discrimination

Evidence

Using the procedure of measuring psycho acoustical tuning curves for hearing-impaired listeners, the reduction of the hearing system’s frequency selectivity can be estimated. Frequency resolution, as measured for normally hearing subjects, is necessary for good speech discrimination. It is understandable that speech discrimination often fails in conditions in which very fiat tuning curves are measured, especially in those cases where temporal resolution also fails. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1896