Distortion-product otoacoustic emissions in the common marmoset (Callithrix jacchus): Parameter optimization

Distortion-product otoacoustic emissions (DPOAEs) were measured in a New World primate, the common marmoset (Callithrix jacchus). We determined the optimal primary-tone frequency ratio (f2/f1) to generate DPOAEs of maximal amplitude between 3 and 24 kHz. The optimal f2/f1, determined by varying f2/f1 from 1.02 to 1.40 using equilevel primary tones, decreased with increasing f2 frequency between 3 and 17 kHz, and increased at 24 kHz. The optimal f2/f1 ratio increased with increasing primary-tone levels from 50 to 74 dB SPL. When all stimulus parameters were considered, the mean optimal f2/f1 was 1.224-1.226. Additionally, we determined the effect of reducing L2 below L1. Decreasing L2 below L1 by 0, 5, and 10 dB (f2/f1 = 1.21) minimally affected DPOAE strength. DPOAE levels were stronger in females than males and stronger in the right ear than the left, just as in humans. This study is the first to measure OAEs in the marmoset, and the results indicate that the effect of varying the frequency ratio and primary-tone level difference on marmoset DPOAEs is similar to the reported effects in humans and Old World primates.