Psychoacoustics of normal and impaired hearing.

Recent developments in the field of psychoacoustics are presented, focusing on areas which have application in the diagnosis and understanding of impaired hearing. Cochlear hearing loss often results in a loss of the compressive non-linearity that operates in normal ears; this loss is probably the main cause of loudness recruitment. Forward masking can be used as a tool to assess the strength of cochlear compression in human listeners. Hearing impairment can sometimes be associated with complete loss of function of inner hair cells over a certain region of the cochlea, resulting in a 'dead region'. Two psychoacoustic methods for detecting dead regions and defining their limits are described. The implications of the results for fitting hearing aids are discussed. Finally, the effect of cochlear hearing loss on the perception of rapid sequences of sounds (stream segregation) is described.