Resolution in azimuth sound localization in the Mongolian gerbil (Meriones unguiculatus)

Abstract

Minimum resolvable angles (MRAs) for sound localization in azimuth in the gerbil were determined in a behavioral study using tones, 300-Hz bands of noise centered at frequencies between 500 Hz and 8 kHz and broad-band noise of on average 60 dB SPL overall level. Using the method of constant stimuli, seven gerbils were trained in a two-alternative-forced-choice procedure to indicate if sounds were presented to them from the left or from the right by choosing the left or right arm of a Y-shaped cage. The MRA is the minimum angle between two loudspeaker locations that the gerbils discriminated. Animals were either stimulated from the front (N=4) or from the back (N=3). The MRA for broad-band noise randomly varying in level by +/- 6 dB was 23 degrees and 45 degrees for gerbils stimulated from the front or back, respectively. Generally a gerbil's MRA for tones declined up to 2 kHz reaching 20 degrees and 31 degrees for gerbils stimulated from the front or back, respectively, and the MRA was generally increased above this frequency. Results for narrow-band noise stimuli were similar. Results are discussed with respect to the available interaural cues and physiological mechanisms of sound localization in the gerbil.