Is acoustic evaluation in a non-primate mammal, the tree shrew, affected by context?

Sound categorisation plays a crucial role for processing ecological and social stimuli in a species' natural environment. To explore the discrimination and evaluation of sound stimuli in human babies and nonhuman primates, a reciprocal habituation-dishabituation paradigm has been successfully introduced into auditory research. We applied the reciprocal paradigm for the first time to a non-primate mammal, the tree shrew (Tupaia belangeri), to examine to what extent non-primate mammals share the ability to evaluate communication calls with primates. Playback stimuli were three types of communication calls, differing distinctively in context and acoustic structure, as well as two artificial control sounds, differing solely in frequency. We assessed the attention towards the playback stimuli by the latency to respond to the test stimulus. Subjects evaluated pairs of communication call types as well as the artificial playback stimuli. Attention towards the test stimuli differed significantly in strength for one pair of communication calls, with subjects dishabituating faster to one category than the other. The comparison of a second pair of communication calls did not show significant differences. Interestingly, subjects also evaluated the artificial control sounds. Findings are only partly in line with results on human and non-human primates. They provided first evidence that in non-primate mammals acoustic evaluation is not solely affected by the sound-associated context but is also linked to unusualness and acoustic cues, such as peak frequency.