title: [Is the middle ear the first filter of frequency selectivity?].
abstract: OBJECTIVE
  The cochlea has traditionally been considered as the first frequency selection filter in the auditory pathway due to the contraction of its external ciliated cells. Yet, much evidence has emerged from work carried out during experiments with animals, some of which is anatomical (connections between the auditory pathway and motor nuclei of the middle ear muscles) and other physiological, which indicates that the middle ear might be the first filter through which specific sounds from noisy environments may initially be isolated.
  
  
  METHODS
  In cooperation with the Department of Mechanical Engineering of the Technical School of Industrial Engineering at the University of Valladolid (UVa) we have developed and refined a new admittance meter capable of evaluating changes in impedance that occur in the human middle ear depending on frequency. Using this device we have measured variation in impedance in 7 otologically healthy volunteers submitted to a varied range of sound environments.
  
  
  RESULTS
  We have found that hearing impedance is not constant but rather that the attention offered by the examined subjects when following a conversation in a noisy environment leads to variations in hearing impedance at high frequencies.
  
  
  CONCLUSIONS
  In the light of these findings we feel that the middle ear does not play a merely passive role in hearing but rather that the contraction of the endotympanic muscles makes possible variations in impedance such that the resonance frequency of the ear shifts towards higher frequencies, thus enhancing sound discrimination in noisy environments.
authors.affiliation: Hospital Universitario Del Río Hortega, Servicio de Otorrinolaringología, Universidad de Valladolid, Valladolid, España. lvallejoval@telefonica.net
authors.forename: Luis Angel
authors.initials: LA
authors.lastname: Vallejo
authors.forename: Antonio
authors.initials: A
authors.lastname: Hidalgo
authors.forename: Fernando
authors.initials: F
authors.lastname: Lobo
authors.forename: María Antonia
authors.initials: MA
authors.lastname: Tesorero
authors.forename: Elisa
authors.initials: E
authors.lastname: Gil-Carcedo
authors.forename: Elena
authors.initials: E
authors.lastname: Sánchez
authors.forename: Luis M
authors.initials: LM
authors.lastname: Gil-Carcedo
mesh_terms: D000158:Acoustic Impedance Tests / Q000295:instrumentation; D055592:Biophysical Phenomena; D004432:Ear, Middle / Q000502:physiology*; D004867:Equipment Design; D006801:Humans