<P> Both CF and FM bats have specialized inner ears which allow them to hear sounds in the ultrasonic range, far outside the range of human hearing . Although in most other aspects, the bat's auditory organs are similar to those of most other mammals, certain bats (horseshoe bats, Rhinolophus spp. and the moustached bat, Pteronotus parnelii) with a constant frequency (CF) component to their call (known as high duty cycle bats) do have a few additional adaptations for detecting the predominant frequency (and harmonics) of the CF vocalization . These include a narrow frequency "tuning" of the inner ear organs, with an especially large area responding to the frequency of the bat's returning echoes . </P> <P> The basilar membrane within the cochlea contains the first of these specializations for echo information processing . In bats that use CF signals, the section of membrane that responds to the frequency of returning echoes is much larger than the region of response for any other frequency . For example, in the greater horseshoe bat, Rhinolophus ferrumequinum, there is a disproportionately lengthened and thickened section of the membrane that responds to sounds around 83 kHz, the constant frequency of the echo produced by the bat's call . This area of high sensitivity to a specific, narrow range of frequency is known as an "acoustic fovea". </P> <P> Odontocetes (toothed whales and dolphins) have similar cochlear specializations to those found in bats . Odontocetes also have the highest neural investment of any cochleae reported to date with ratios of greater than 1500 ganglion cells / mm of basilar membrane . </P> <P> Further along the auditory pathway, the movement of the basilar membrane results in the stimulation of primary auditory neurons . Many of these neurons are specifically "tuned" (respond most strongly) to the narrow frequency range of returning echoes of CF calls . Because of the large size of the acoustic fovea, the number of neurons responding to this region, and thus to the echo frequency, is especially high . </P>

Echo location used by animals uses what type of wave interaction