Frequency and intensity difference limens and nonlinearities in the ear of the housemouse (Mus musculus)
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- Ehret, G. J. Comp. Physiol. (1975) 102: 321. doi:10.1007/BF01464344
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Frequency and intensity difference limens were determined for the housemouse (Mus musculus, outbred strain NMRI) between 1 kHz and 80 kHz and for sound pressure levels (SPLs) between 15 dB and 100 dB re. 0.0002 dyn/cm2.
The frequency difference limens (Δfs) decrease linearly with increasing SPL. The slopes (a) of the regression lines are frequency dependent (¦a¦=p·/tfq;p andq are constants) with ¦a¦ being maximal at 15 kHz. An intensity independent level of the smallest noticeable frequency differenceΔfm is reached at a definite SPL (LΔfm) which is always 60 dB above the absolute hearing threshold (LHS) at each frequency tested (LΔfm-LHS=const.). The relative frequency difference limenΔfm/f was nearly constant and equal to 0.85%.
The intensity difference limens (ΔLs) decrease with increasing SPL. The interdependence can be approximated by a linear or a power function (ΔLs=−0.05·SL+7;ΔLs=0.04· SL+120·SL−1; SL=sensation level). The difference limens (ΔLs) are frequency dependent (ΔLs=d·fe·SL) at low sensation levels. The equationΔI=g·I0.95 (I=sound intensity) shows a near miss of Weber's law. The relative averaged difference limen (ΔLs/SL) amounts to 6.7% at 60 dB SL.
The results agree well with a model of a spectrum-excitation-transformation on the basilar membrane (Maiwald, 1967). In addition, a new frequency dependent nonlinearity of the mammalian ear is defined. It influences frequency and intensity discrimination in the same manner and can be expressed in a power function of the frequency summarized in the proportion:Δf∼ΔLs∼fz·L.
Comparative aspects of difference limens in man and other mammals are discussed.