Sensitivity of the mouse to changes in azimuthal sound location: Angular separation, spectral composition, and sound level.

Abstract

Auditory spatial acuity was measured in mice using prepulse inhibition (PPI) of the acoustic startle reflex as the indicator response for stimulus detection. The prepulse was a "speaker swap" (SSwap), shifting a noise between two speakers located along the azimuth. Their angular separation, and the spectral composition and sound level of the noise were varied, as was the interstimulus interval (ISI) between SSwap and acoustic startle reflex elicitation. In Experiment 1 a 180 degrees SSwap of wide band noise (WBN) was compared with WBN Onset and Offset. SSwap and WBN Onset had near equal effects, but less than Offset. In Experiment 2 WBN SSwap was measured with speaker separations of 15, 22.5, 45, and 90 degrees . Asymptotic level and the growth rate of PPI increased with increased separation from 15 to 90 degrees , but even the 15 degrees SSwap provided significant PPI for the mean performance of the group. SSwap in Experiment 3 used octave band noise (2-4, 4-8, 8-16, or 16-32 kHz) and separations of 7.5 to 180 degrees . SSwap was most effective for the highest frequencies, with no significant PPI for SSwap below 8-16 kHz, or for separations of 7.5 degrees . In Experiment 4 SSwap had WBN sound levels from 40 to 78 dB SPL, and separations of 22.5, 45, 90, and 180 degrees : PPI increased with level, this effect varying with ISI and angular separation. These experiments extend the prior findings on sound localization in mice, and the dependence of PPI on ISI adds a reaction time-like dimension to this behavioral analysis.