Interaural Intensity Difference Cues Research Articles

Parameter study of time-delay magnification in a biologically inspired, mechanically coupled acoustic sensor array.

Sound source localization uses interaural time difference (ITD) or interaural intensity difference cues, and most of the methods based on ITD are limited by the aperture of array. However, a kind of parasitoid fly called Ormia ochracea with coupled ears has a remarkable ability to localize calling of crickets regardless of the fly's small body size. The structure of fly's ear is generalized, and a multi-dimensional coupled system with an acoustic sensor array is proposed. The magnification factor of the phase difference in this system, which can be used to describe the ITD changes of signals from the coupled system, is chosen as the kernel parameter to measure the effect of coupling. The coupled system is optimized by choosing appropriate physical parameters such that the degree of magnification does not vary with angle of incidence. The simulation results demonstrate that the time delay between two signals increases by the coupled system, and the magnification factor remains stable as expected. Compared with the traditional general cross-correlation method, the localization error of the coupled system is reduced.

Spiking neural network model of sound localization using the interaural intensity difference.

In this paper, a spiking neural network (SNN) architecture to simulate the sound localization ability of the mammalian auditory pathways using the interaural intensity difference cue is presented. The lateral superior olive was the inspiration for the architecture, which required the integration of an auditory periphery (cochlea) model and a model of the medial nucleus of the trapezoid body. The SNN uses leaky integrate-and-fire excitatory and inhibitory spiking neurons, facilitating synapses and receptive fields. Experimentally derived head-related transfer function (HRTF) acoustical data from adult domestic cats were employed to train and validate the localization ability of the architecture, training used the supervised learning algorithm called the remote supervision method to determine the azimuthal angles. The experimental results demonstrate that the architecture performs best when it is localizing high-frequency sound data in agreement with the biology, and also shows a high degree of robustness when the HRTF acoustical data is corrupted by noise.

Use of binaural cues for sound localization in large and small non-echolocating bats: Eidolon helvum and Cynopterus brachyotis

The authors determined the ability of two old-world non-echolocating bats, Eidolon helvum and Cynopterus brachyotis, to use binaural time and intensity difference cues for localization. The bats were trained to localize pure tones throughout most of their hearing range from loudspeakers located 30 degrees to the left and right of midline. Both species easily localized high frequency tones, indicating they could use the interaural intensity difference cue. However, neither was able to localize low frequency tones even when the tones were amplitude modulated thereby indicating that they could not use ongoing phase difference cues. The authors now know of eight mammals that do not use binaural phase cues for localization, and some possible reasons for this inability are explored.

Use of binaural cues for sound localization in two species of Phyllostomidae: The Greater spear-nosed bat (Phyllostomus hastatus) and the Short-tailed fruit bat (Carollia perspicillata).

Unlike humans, not all mammals use both of the binaural cues for sound localization. Whether an animal uses these cues can be determined by testing its ability to localize pure tones; specifically, low frequencies are localized using time-difference cues, and high frequencies are localized using intensity-difference cues. We determined the ability to use binaural cues in 2 New World bats, Phyllostomus hastatus, large omnivores, and Carollia perspicillata, small frugivores, by testing their tone-localization ability using a conditioned avoidance procedure. Both species easily localized high-frequency tones, indicating that they could use the interaural intensity-difference cue. However, neither species was able to use the phase-difference cue to localize either low-frequency pure tones or amplitude-modulated tones (which provided an envelope for additional time analysis). We now know of 3 bat species that cannot use binaural time cues and 2 that can. Further exploration of localization in bats may provide insight into the neural analysis of time cues in species that do not hear low frequencies.

Computational Auditory Scene Analysis: Principles, Algorithms and Applications

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Binaural Interaction in the Human Frequency-Following Response: Effects of Interaural Intensity Difference

The binaural interaction component (BIC) of the 500-Hz human frequency-following response (FFR) was evaluated as a function of interaural intensity difference (IID) using a lateralization paradigm. The robust FFR interaction component (FFR-BIC) was shown to decrease systematically with increasing IID with no discernible FFR-BIC for IID values larger than about 20 dB. These findings are similar to that observed for the high-frequency auditory brainstem response interaction component (ABR-BIC). Thus, like the ABR-BIC, the FFR-BIC may be correlated with binaural fusion and the perceived location of the fused image of the sound. These results taken together suggest that the binaural neurons in the brainstem are able to utilize IID cues presented in both low-frequency and high-frequency sounds.

Sound localization in chinchillas. I: Left/right discriminations

The ability of chinchillas to localize sound was examined behaviorally using a conditioned avoidance procedure in which the animals were trained to discriminate left from right sound sources. Their minimum audible angle was 15.6° for 100-ms broadband noise making them one of the more accurate rodents, although they are not as accurate as primates and carnivores. Thresholds obtained for filtered noise stimuli demonstrated that chinchillas are equally accurate in localizing either low- or high-frequency noise. Further, they are able to use both interaural phase-difference and interaural intensity-difference cues as demonstrated by their ability to localize both low- and high-frequency pure tones. Finally, analysis of the chinchilla retina supports the hypothesis that the role of auditory localization in directing the eyes to sound sources played a role in the evolution of auditory spatial perception.