Abstract
Mice display a wide repertoire of vocalizations that varies with age, sex, and context. Especially during courtship, mice emit ultrasonic vocalizations (USVs) of high complexity, whose detailed structure is poorly understood. As animals of both sexes vocalize, the study of social vocalizations requires attributing single USVs to individuals. The state-of-the-art in sound localization for USVs allows spatial localization at centimeter resolution, however, animals interact at closer ranges, involving tactile, snout-snout exploration. Hence, improved algorithms are required to reliably assign USVs. We develop multiple solutions to USV localization, and derive an analytical solution for arbitrary vertical microphone positions. The algorithms are compared on wideband acoustic noise and single mouse vocalizations, and applied to social interactions with optically tracked mouse positions. A novel, (frequency) envelope weighted generalised cross-correlation outperforms classical cross-correlation techniques. It achieves a median error of ~1.4 mm for noise and ~4–8.5 mm for vocalizations. Using this algorithms in combination with a level criterion, we can improve the assignment for interacting mice. We report significant differences in mean USV properties between CBA mice of different sexes during social interaction. Hence, the improved USV attribution to individuals lays the basis for a deeper understanding of social vocalizations, in particular sequences of USVs.
Highlights
Mice emit complex and non-random ultrasonic vocalizations (USV) during social interactions[1,2,3,4]
Social interaction paradigms with male-male pairings may rule out the presence of female USVs8, but these calls can no longer be compared to male courtship calls, due to changes in behavioral state
We developed and experimentally evaluated a range of sound source localization algorithms in the context of mouse vocalizations, especially during social interactions
Summary
Mice emit complex and non-random ultrasonic vocalizations (USV) during social interactions[1,2,3,4] These vocalizations are strongly modulated on different levels by a variety of contextual determinants, such as age, genetic background, behavioural state and to a lesser extent by sex[5]. It has been shown that playback of different types of USVs can elicit different responses in the recipient mouse[13] This suggests that mice are able to adapt their vocal behaviour in a context-dependent manner and that these modifications may convey information[14]. A recent study shows that female mice do vocalize during social interaction with males, in between the chases of courtship behaviour[33] For this purpose, a microphone array was used in addition to a sound source localization method[34]. While the present results are obtained on a 1D setup using two microphones, the methods presented can in principle be generalised to 2D or 3D contexts by adding microphones and slightly generalizing the analytical correction method
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