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

Abstract

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 (f(2)/f(1)) to generate DPOAEs of maximal amplitude between 3 and 24 kHz. The optimal f(2)/f(1), determined by varying f(2)/f(1) from 1.02 to 1.40 using equilevel primary tones, decreased with increasing f(2) frequency between 3 and 17 kHz, and increased at 24 kHz. The optimal f(2)/f(1) ratio increased with increasing primary-tone levels from 50 to 74 dB SPL. When all stimulus parameters were considered, the mean optimal f(2)/f(1) was 1.224-1.226. Additionally, we determined the effect of reducing L(2) below L(1). Decreasing L(2) below L(1) by 0, 5, and 10 dB (f(2)/f(1)=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.

Age-related shifts in distortion product otoacoustic emissions peak-ratios and amplitude modulation spectra

“…To determine the slopes of individual I/O functions, we fitted a linear-regression equation to the linear portion of the functions (Valero, Pasanen et al 2008) and termed it low-level slope. In most animals, the linear growth occurred between L1= 50 to 60 or 65 dB SPL, and the functions tended to saturate at 70–75 dB SPL.…”

“…These correspond to stimulus-frequency ratios (f2/f1 ratios) of 1.01–1.45. The f2/f1 range was chosen because it encompasses the commonly used ratio, which is 1.22, in most DPOAE studies (Harris, Lonsbury-Martin et al 1989, Lasky, Snodgrass et al 1995, Valero, Pasanen et al 2008). The stimulus level of f1, L1, was fixed at both 75 dB SPL and 20 dB above animals’ hearing threshold at 8 kHz.…”

“…DPOAE amplitudes are dependent upon the stimulus-frequency ratio (f2/f1) of the two tones (Abdala 1996, Dhar, Long et al 2005). It has been reported that, on average, an f2/f1 ratio of 1.22 evokes the largest DPOAEs in human adults (Abdala 1996) and in marmosets (Lasky, Snodgrass et al 1995, Valero, Pasanen et al 2008). “Peak-ratio” used in this paper is defined as the f2/f1 ratio that evokes the largest DPOAEs.…”

“…We aim to test the hypothesis by performing two experiments. In experiment 1, we investigated age-related differences of peak-ratio using two pure tones with various stimulus-frequency ratios to elicit DPOAEs (Harris, Lonsbury-Martin et al 1989, Dhar, Long et al 2005, Valero, Pasanen et al 2008). In experiment 2, we assessed AM detectability of basilar membrane vibration in young and aged rats using a few combinations of one pure tone and one AM tone, in which the AM depth of the AM tone was varied systematically at different degrees.…”

The Marmoset as a Model of Aging and Age-Related Diseases

“…Anatomical evidence supporting the similarity of the marmoset cochlea to that of humans comes from the work of Spatz and Lohle (1995), which indicated that the marmoset cochlea has 2½ turns, as in humans. Physiological data supporting this similarity come from a recent study on the measurement of otoacoustic emissions (sounds emitted by the ear in response to stimulation): using a noninvasive technique that measures outer hair cell function Valero and colleagues (2008) showed that the acoustical stimulation parameters required to elicit the strongest emissions are similar to those of humans and Old World primates. Taken together, these studies suggest that cochlear parameters may be largely conserved in humans and nonhuman primates.…”