The auditory fovea of the barn owl - no correlation with enhanced frequency resolution.

Köppl, C.; Klump, G. M.; Taschenberger, G.; Dyson, M. and Manley, G. A. (1998). The auditory fovea of the barn owl - no correlation with enhanced frequency resolution. In: Palmer, A. R.; Rees, A.; Summerfield, A. Q. and Meddis, R. eds. Psychophysical and Physiological Advances in Hearing. London: Whurr, pp. 153–159.


The barn owl (Tyto alba) is a nocturnal hunter that relies on passive acoustic localization of its prey. May specializations associated with prey localization are known at all levels of the auditory system (e.g. Konishi, 1993). A striking feature of the barn owl's cochlea or basilar papilla is the highly unusual distribution of frequencies along the epithelium. In contrast to the common pattern of approximately equal lengths of the cochlea devoted to each octave (e.g. Greenwood, 1990), the barn owl provides a rapidly increasing amount of space for frequencies above 2 kHz. More than half of the basilar papilla's length is devoted to the narrow band between 5 and 10 kHz (Köppl et al., 1993). In analogy to similar cases of cochlear spatial overrepresentation in several mammals (Kössl and Vater, 1985; Vater et al., 1985; Müller et al., 1992), this has been termed an auditory fovea.

In the horseshoe and mustached bats, such foveal representations of certain narrow frequency ranges are partly accompanied by a dramatic increase in frequency resolution, that is seen in neural tuning (Suga et al., 1976; Kössl and Vater, 1990), in the generation and suppression of otoacoustic emissions (Kössl, 1994; Frank and Kössl, 1995) and in psychophysical measures of frequency selectivity (Long, 1980). This is consistent with models attributing psychophysical measures of frequency selectivity to the spatial representation of frequencies along the cochlea, such as the equal-distance hypothesis (review in Greenwood, 1991).

We investigated whether, in the barn owl, a correlation between frequency selectivity and cochlear spatial representation is present. Frequency selectivity was evaluated at the level of the basilar papilla and auditory nerve, as well as psychophysically. If a relationship with spatial representation exists, the cochlear map predicts that frequency filter bandwidths should first rise about two-fold from the lowest frequencies towards 4 kHz and then drop sharply towards 10 kHz.

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