Abstract
Animals recognize biologically relevant sounds, such as the non-harmonic sounds made by some predators, and respond with adaptive behaviors, such as escaping. To clarify which acoustic parameters are used for identifying non-harmonic, noise-like, broadband sounds, guinea pigs were conditioned to a natural target sound by introducing a novel training procedure in which 2 or 3 guinea pigs in a group competed for food. A set of distinct behavioral reactions was reliably induced almost exclusively to the target sound in a 2-week operant training. When fully conditioned, individual animals were separately tested for recognition of a set of target-like sounds that had been modified from the target sound, with spectral ranges eliminated or with fine or coarse temporal structures altered. The results show that guinea pigs are able to identify the noise-like non-harmonic natural sounds by relying on gross spectral compositions and/or fine temporal structures, just as birds are thought to do in the recognition of harmonic birdsongs. These findings are discussed with regard to similarities and dissimilarities to harmonic sound recognition. The results suggest that similar but not identical processing that requires different time scales might be used to recognize harmonic and non-harmonic sounds, at least in small mammals.
Highlights
Animal habitats are rich in environmental sounds
The stimulus set used for the training consisted of 8 different sounds (1 T and 7 NT sounds), which were repeated times per session with their order randomized in every set
Once guinea pigs were conditioned to the The footstep sound (T sound), distinctive and presumably innate behavioral reactions were reliably evoked after the T sound onset but prior to feeding (Fig. 3A)
Summary
Environmental natural sounds can be classified into two global groups based on their spectral structures: harmonic and non-harmonic sounds [1]. Animal calls, and birdsongs are generally harmonic in structure, last a relatively long time, and are used frequently for conspecific communication [2,3,4,5]. Ambient sounds that animals are exposed to in their environments are generally non-harmonic and of short duration. Some of these sounds may gain biological significance, most likely as a consequence of exposure or learning. Nonharmonic, noise-like sounds produced by movements of approaching predators can induce adaptive responses, such as escaping or freezing, in the listening prey. Animals in captivity can anticipate food or water from various sounds made by animal keepers approaching the cage, and these sounds may become attractive signals to these animals
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