[Pathophysiology of auditory and speech perception].

Auditory perception or hearing can be defined as the interpretation of sensory evidence, produced by the ears in response to sound, in terms of the events that caused the sound. We do not hear a window but we may hear a window closing. We do not hear a dog but we may hear a dog barking. And we do not hear a person but we may hear a person talking. Hearing impairment can result in anxiety or stress in everyday life. Pure-tone hearing loss (or threshold shift) is a measure of hearing impairment. Aging and excessive noise are the main causes of hearing impairment. Speech perception is another concept. The difference with the former is best illustrated by the disabled individual declaring "I can hear that someone is talking to me, but I don't understand what she says". Being unable to understand easily and clearly significant others, especially in understanding speech in a noisy environment, can give rise to considerable psychosocial and professional consequences (disability). Presbycusis is the decline in hearing sensitivity caused by the aging process at different levels of the auditory system. However, it is difficult to isolate age effects from other contributors to age-related hearing loss such as noise damage, genetic susceptibility, inflammatory otologic disorders, and ototoxic agents. Therefore, presbycusis and age-related hearing loss are often used synonymously. In this report pathophysiology is mostly described with regard to presbycusis, and the main peripheral types of presbycusis (sensory or Corti organ-related, strial, and neural) are summarized. An original experimental model of strial presbycusis, based on chronic application of furosemide at the round window, is further described. Central presbycusis is mainly determined by degeneration secondary to peripheral impairment (concept of deafferentation). Central auditory changes typically affect speed of processing and result in poorer speech understanding in noise or with rapid or degraded speech. Last, age-related cognitive factors can be associated to peripheral hearing impairment and increase disability in speech understanding in noise.