Frequency and intensity difference limens and nonlinearities in the ear of the housemouse (Mus musculus)

Abstract

1. 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. 2. 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%. 3. 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. 4. 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. 5. Comparative aspects of difference limens in man and other mammals are discussed.