Behavioral Sensitivity to Broadband Binaural Localization Cues in the Ferret

Abstract

Although the ferret has become an important model species for studying both fundamental and clinical aspects of spatial hearing, previous behavioral work has focused on studies of sound localization and spatial release from masking in the free field. This makes it difficult to tease apart the role played by different spatial cues. In humans and other species, interaural time differences (ITDs) and interaural level differences (ILDs) play a critical role in sound localization in the azimuthal plane and also facilitate sound source separation in noisy environments. In this study, we used a range of broadband noise stimuli presented via customized earphones to measure ITD and ILD sensitivity in the ferret. Our behavioral data show that ferrets are extremely sensitive to changes in either binaural cue, with levels of performance approximating that found in humans. The measured thresholds were relatively stable despite extensive and prolonged (>16 weeks) testing on ITD and ILD tasks with broadband stimuli. For both cues, sensitivity was reduced at shorter durations. In addition, subtle effects of changing the stimulus envelope were observed on ITD, but not ILD, thresholds. Sensitivity to these cues also differed in other ways. Whereas ILD sensitivity was unaffected by changes in average binaural level or interaural correlation, the same manipulations produced much larger effects on ITD sensitivity, with thresholds declining when either of these parameters was reduced. The binaural sensitivity measured in this study can largely account for the ability of ferrets to localize broadband stimuli in the azimuthal plane. Our results are also broadly consistent with data from humans and confirm the ferret as an excellent experimental model for studying spatial hearing.

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

“…This value is comparable to reports in rabbit (50-60 µs, Ebert et al 2008), ferret (23 µs, Keating et al 2013), and cat (~30 µs, Wakeford and Robinson 1974). By assuming guinea pigs have a similar ITD discrimination threshold of 55 µs, and taking into account the average ITD slope of 3 µs/º reported here, we can predict a low-frequency spatial discrimination ability of 18.3º, slightly broader than reported in chinchilla.…”

“…However, by analyzing the range of cues available to guinea pig, and comparing these values to other similar species, we can make some conservative predictions regarding the behavioral ability of guinea pig in localizing and discriminating sounds in space. Previous studies have shown minimum ILD discrimination in humans, primates, cats and ferrets between 1–4 dB (Houben and Gourevitch 1979; Keating et al 2013; Mills 1960; Scott et al 2007; Wakeford and Robinson 1974) (see Tsai et al 2010 for review). Similarly, consideration of acoustic measurements from our lab (Koka et al 2011) along with psychophysical data (Heffner et al 1994) suggest that chinchillas should be able to discriminate ILDs of at least 4 dB, which coincides with the 13.7º spatial acuity reported by Heffner et al (1994) for broadband noise high-pass filtered at 8 kHz.…”

Slow Temporal Integration Enables Robust Neural Coding and Perception of a Cue to Sound Source Location

“…Behavioral ILD sensitivity is consistent with several-millisecond windows of E-I interaction Previous psychophysical measurements in human (Hartmann and Constan, 2002) and animal subjects (Egnor, 2001;Keating et al, 2013) indicated that psychophysical detection of ILDs was essentially unaffected by decorrelation. These experiments used broadband stimuli that conveyed information in many auditory filters simultaneously and did not assess the usability of suprathreshold information (e.g., for lateralization).…”

“…While chinchillas were selected for the audiometric similarity to humans, including a similar range of hearing (Heffner and Heffner, 1991) and demonstrated use of both ITD and ILD cues for sound localization (Heffner et al, 1994), such cross-species comparisons are, of course, limiting. The effect of interaural decorrelation on ILD sensitivity appears to be similarly negligible in humans (present study; Hartmann and Constan, 2002) and ferrets (Keating et al, 2013), and also barn owls (Egnor, 2001), but behavioral data from chinchilla or other animal models could be informative, if only to further confirm the lack of an effect. Although aspects of our behavioral and midbrain neural data were similar, other explanations for integrative ILD sensitivity (e.g., involving downstream mechanisms we did not consider) could certainly be proposed (Stecker et al, 2015).…”

“…This ϳ1 ms temporal window is conserved across studied mammalian species, including cat (Joris and Yin, 1995), bat (Park, 1998), rat (Irvine et al, 2001), and gerbil (T. P. Franken, personal communication). In contrast, human and animal behavioral ILD sensitivity appears to be robust to interaural temporal asynchrony: ILD discrimination is nearly identical for interaurally correlated (identical) and uncorrelated (independent) noise (human, Hartmann and Constan, 2002; ferret, Keating et al, 2013).…”