Localization of tones and noise in the horizontal plane by unrestrained house mice (Mus musculus)

Abstract

House mice (Mus musculus, outbred strain NMRI) were trained to locate loudspeakers at the margin of a wire-mesh covered circular platform. Sound signals were tone bursts of 1, 15, 50 and 80 kHz and noise bursts (bandwidth 15–80 kHz). Localization acuity as represented by orientation angles (alpha) toward the speaker was determined at 5 radial distances from the centre of the platform. If the animals could localize under closed-loop conditions (with repetitive stimulation), the distributions of (alpha) showed a significant peak at the speaker position (0 degrees) and mean orientation angles (alpha) for the different stimuli all varied around 0 degrees. Distributions of (alpha) from open-loop tests were not peaked, i.e. mice did not localize the sound source. We calculated the median angle (beta) of the distributions of orientated runs and used (beta) as a measure for the accuracy of localization. Smallest values of beta were 12 degrees for 1 kHz, 15 degrees for 15 kHz, 9.5 degrees for 50 kHz, 8.5 degrees for 80 kHz tone bursts and 7 degrees for the noise bursts. The results are discussed in relation to possible localization mechanisms in mice.