Are horses lateralized for the auditory processing of whinnies varying in their degree of familiarity?

International audienceIn the past, studies on laterality of auditory processing focused mainly on primates and birds.Communicative signals' species-specificity has been largely investigated as a factorsusceptible to influence hemispheric specialization, but little is known concerning the impactof social familiarity. Here, we tested the influence of the degree of emitter-receiver familiarityon auditory laterality in domestic horses, using the widely used head orientation behaviouralparadigm. As the species shows visible reactions to sound, with one or two ears movingtowards a sound source, we integrated ear orientation as a further behavioural variable. Wecould therefore dissociate visual implication, usually integrated on the traditional measure ofhead orientation, from auditory laterality. By comparing responses to the playbacks ofdifferent conspecific whinnies (group member/familiar neighbour/stranger), we demonstrateda left hemisphere preference for neighbour calls while no preference was found for groupmember or stranger calls. An opposite pattern of ear side preference appeared for neighbourvs stranger calls. To our knowledge, these results are the first to demonstrate auditorylaterality in an ungulate species. They support the idea that not only a call's social value, butalso the degree of attention of the listener could influence auditory laterality