The acoustical cues to sound location in the guinea pig (Cavia porcellus)

Abstract

There are three main acoustical cues to sound location, each attributable to space-and frequency-dependent filtering of the propagating sound waves by the outer ears, head, and torso: Interaural differences in time (ITD) and level (ILD) as well as monaural spectral shape cues. While the guinea pig has been a common model for studying the anatomy, physiology, and behavior of binaural and spatial hearing, extensive measurements of their available acoustical cues are lacking. Here, these cues were determined from directional transfer functions (DTFs), the directional components of the head-related transfer functions, for eleven adult guinea pigs. In the frontal hemisphere, monaural spectral notches were present for frequencies from ~10 to 20 kHz; in general, the notch frequency increased with increasing sound source elevation and in azimuth toward the contralateral ear. The maximum ITDs calculated from low-pass filtered (2 kHz cutoff frequency) DTFs were ~250 µs, whereas the maximum ITD measured with low frequency tone pips was over 320 µs. A spherical head model underestimates ITD magnitude under normal conditions, but closely approximates values when the pinnae were removed. Interaural level differences (ILDs) strongly depended on location and frequency; maximum ILDs were < 10 dB for frequencies < 4 kHz and were as large as 40 dB for frequencies > 10 kHz. Removal of the pinna reduced the depth and sharpness of spectral notches, altered the acoustical axis, and reduced the acoustical gain, ITDs, and ILDs; however, spectral shape features and acoustical gain were not completely eliminated, suggesting a substantial contribution of the head and torso in altering the sounds present at the tympanic membrane.

The Neural Substrate for Binaural Masking Level Differences in the Auditory Cortex

“…For both the noise and tone, the majority of units had best ITDs Ͻ350 s within the contralateral hemifield. This is comparable with the range of ITDs calculated from head-related transfer functions (HRTFs) measured acoustically (Sterbing et al, 2003;Greene et al, 2014). Only 7 (7%) of the 99 delay sensitive units were trough types (Yin and Kuwada, 1983) (i.e., an approximately constant response across ITD except for a dip at the "worst" phase).…”

“…The representations of the neuronal responses shown in Figure 10 are highly weighted toward the most commonly measured best ITDs (50 -350 s); very few neurons in the present dataset had best ITDs outside of this range, which corresponds to the measured range of ecologically available ITDs (Sterbing et al, 2003;Greene et al, 2014).…”

Development of the head, pinnae, and acoustical cues to sound location in a precocial species, the guinea pig ( Cavia porcellus )

“…They are also popular models for studies of middle (Guan and Gan, 2011; Lee et al, 2014) and inner (Chen et al, 2014) ear mechanics likely because the guinea pig is audiometrically similar to humans in that they hear sounds over comparable ranges of frequencies (Heffner et al, 1971; Syka et al, 2000). Guinea pigs also share similar pinna features (Greene et al, 2014) as humans–unlike many other commonly used animal models (i.e., cat, chinchilla, bat) with upright, conical pinna, guinea pigs have more oval-shaped, “flattened” ears positioned on either side of the head. Finally, also like humans, guinea pigs are precocial with functional central and peripheral auditory systems at birth (Sedlácek, 1976).…”

“…Aside from measurements in the adult guinea pig (Carlile and Pettigrew, 1987; Greene et al, 2014; Sterbing, 2003), there has not been a systematic study of the monaural and binaural acoustic cues to location in the developing animal. In order to utilize the guinea pig as a model for auditory development, we must understand the sound localization cues available to the auditory system at different stages of development.…”

Representation of Multidimensional Stimuli: Quantifying the Most Informative Stimulus Dimension from Neural Responses

“…In general, lowfrequency sources are localized via interaural time differences (ITD), whereas high-frequency sources are localized via interaural level differences (ILD;Rayleigh, 1907; for measurement of cues in the species considered in the present paper, see Koka et al, 2011;Greene et al, 2014). Sensitivity to ILD relies on comparison of sound level at the two ears, which is also of course directly affected by the level of the sound source (ABL; Fig.…”