Threshold minima and maxima in the behavioral audiograms of the bats Artibeus jamaicensis and Eptesicus fuscus are not produced by cochlear mechanics.
Behavioral audiograms of Artibeus jamaicensis and Eptesicus fuscus are characterized by two threshold minima separated by a threshold maximum at 40 kHz, for A. jamaicensis, and 45 kHz, for E. fuscus [Koay, G., Heffner, H.E., Heffner R.S., 1997. Audiogram of the big brown bat (Eptesicus fuscus). Hear. Res. 105, 202-210; Heffner, R.S., Koay, G., Heffner H.E., 2003. Hearing in American leaf-nosed bats. III: Artibeus jamaicensis. Hear. Res. 184, 113-122.]. To investigate whether these characteristics are due to cochlear properties, we recorded distortion product otoacoustic emissions (DPOAEs) and calculated DPOAE threshold curves. We found that in both species cochlear sensitivity, assessed by DPOAE recordings, does not show local threshold maxima. The DPOAE threshold curve calculated for A. jamaicensis reveals a broadly tuned minimum for frequencies between 20 and 50 kHz and the threshold curve of E. fuscus shows a broad sensitive area for frequencies between 15 and 60 kHz. In none of the two species any pronounced threshold irregularities were found. The characteristic pattern of a threshold maximum followed by a minimum observed in behavioral studies seems to be shaped by transfer characteristics of the outer ear and/or neuronal processing in the ascending auditory pathway rather than by cochlear mechanics.
Macías
Silvio
S
Department of Animal and Human Biology, Faculty of Biology, Havana University, calle 25 No. 455 entre J e I, Vedado, CP 10400, Cuidad de La Habana, Cuba. silvio@fbio.uh.cu
Mora
Emanuel C
EC
Coro
Frank
F
Kössl
Manfred
M
D000818:Animals; D001306:Auditory Pathways / Q000502:physiology*; D001309:Auditory Threshold / Q000502:physiology*; D002685:Chiroptera / Q000502:physiology*; D003051:Cochlea / Q000502:physiology*; D005260:Female; D008297:Male; D017084:Otoacoustic Emissions, Spontaneous / Q000502:physiology*