Abstract
In humans, speech perception is lateralized, with the left hemisphere of the brain dominant in processing the communicative content and the right hemisphere dominant in processing the emotional content. However, still little is known about such a division of tasks in other species. We therefore investigated lateralized processing of communicative and emotionally relevant calls in a social mammal, the pig (Sus scrofa). Based on the contralateral connection between ears and hemispheres, we compared the behavioural and cardiac responses of 36 young male pigs during binaural and monaural (left or right) playback to the same sounds. The playback stimuli were calls of social isolation and physical restraint, whose communicative and emotional relevance, respectively, were validated prior to the test by acoustic analyses and during binaural playbacks. There were indications of lateralized processing mainly in the initial detection (left head-turn bias, indicating right hemispheric dominance) of the more emotionally relevant restraint calls. Conversely, there were indications of lateralized processing only in the appraisal (increased attention during playback to the right ear) of the more communicative relevant isolation calls. This implies differential involvement of the hemispheres in the auditory processing of vocalizations in pigs and thereby hints at similarities in the auditory processing of vocal communication in non-human animals and speech in humans. Therefore, these findings provide interesting new insight in the evolution of human language and auditory lateralization.
Highlights
The study of vocal communication in non-human animals can provide useful information to improve our understanding of the evolution of human speech and language (Fitch, 2005; Beckers, 2011)
This hemispheric specialization may have originated from left hemisphere dominance in the auditory perception of conspecific calls in non-human animals
In some species, there are reports of left hemisphere dominance in perceiving heterospecific calls that have communicative relevance, such as for dogs listening to human speech (Ratcliffe and Reby, 2014)
Summary
The study of vocal communication in non-human animals can provide useful information to improve our understanding of the evolution of human speech and language (Fitch, 2005; Beckers, 2011). Research on auditory perception of vocalizations in nonhuman animals can help in tracing the roots of the cortical processing of linguistic and paralinguistic content, such as the emotional state and identity of the sender, in human speech. One of the specific features of human speech perception is that it is dominated by the left hemisphere (Tervaniemi and Hugdahl, 2003). This hemispheric specialization may have originated from left hemisphere dominance in the auditory perception of conspecific calls in non-human animals (reviewed by Ocklenburg et al, 2013). The communicative relevance of conspecific calls may be shaped by experience (Poremba et al, 2013) such that left hemisphere dominance for listening to certain calls may be restricted to some receivers, e.g., mother mice listening to pup calls (Ehret, 1987)
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