Socially dependent auditory laterality in domestic horses (Equus caballus)

Abstract

Laterality is now known to be an ubiquitous phenomenon among the vertebrates. Particularly, laterality of auditory processing has been demonstrated in a variety of species, especially songbirds and primates. Such a hemispheric specialization has been shown to depend on factors such as sound structure, species specificity and types of stimuli. Much less is known on the possible influence of social familiarity although a few studies suggest such an influence. Here we tested the influence of the degree of familiarity on the laterality of the auditory response in the domestic horse. This species is known for its social system and shows visible reactions to sounds, with one or two ears moving towards a sound source. By comparing such responses to the playback of different conspecific whinnies (group member, neighbor and stranger), we could demonstrate a clear left hemisphere (LH) preference for familiar neighbor calls while no preference was found for group member and stranger calls. Yet, we found an opposite pattern of ear side preference for neighbor versus stranger calls. These results are, to our knowledge, the first to demonstrate auditory laterality in an ungulate species. They open further lines of thought on the influence of the social "value" of calls and the listener's arousal on auditory processing and laterality.

Right ear advantage for vocal communication in frogs results from both structural asymmetry and attention modulation

“…Since projections to the midbrain arise primarily from the contralateral auditory periphery, the results obtained here support the hypothesis that right-ear/left-hemispheric superiority for processing communication sounds in frogs is to a significant extent due to structural asymmetries in the way the auditory system processes information. This finding is also in agreement with earlier studies on REA in amniote vertebrates holding a left-hemisphere priority for processing conspecific/neighbor vocalizations [1,[16][17][18][19]24,[52][53][54][55][56][57]. Furthermore, the REA in music frogs has been demonstrated, at least in part, in a preliminary behavioral study using a head orienting task in which the subjects preferentially turned their bodies toward the right while listening to HSA playbacks, but did not show a turning preference in silence (unpublished data).…”

“…lateralization or asymmetry of brain function, has been described in many vertebrate taxa including fish, frogs, reptiles, birds and mammals [1][2][3], as a fundamental aspect of nervous system organization [4]. The left hemisphere is specialized to categorize information and responds to features that are invariant and repeated, while the right domestic horses [18] and rhesus macaques [19]. To explain the observed hemispheric auditory asymmetry, various models have been proposed, including those based on the temporal and spectral structures of communication sounds [20], on an attentional filter termed the double-filtering-by-frequency model [21] and on different temporal integration windows for each hemisphere termed the asymmetric-sampling-in-time model [22,23].…”

The biological significance of acoustic stimuli determines ear preference in the music frog

“…This rightward bias is comparable to results of head orientation studies in other vertebrates (Böye et al, 2005;Basile et al, 2009;Hauser and Andersson, 1994;Reinholz-Trojan et al, 2012;Siniscalchi et al, 2008) and supports the idea that among land vertebrates, most individuals orient the right side of the head towards sound sources when listening to conspecific calls. Recent work on sound localization behavior in gray treefrogs, which differ from music frogs in both habitat and phylogenetic position (Alexander Pyron and Wiens, 2011), showed no consistent tendency to turn rightwards for females in response to male advertisement calls, in either 0 or 180 deg sound presentations (Caldwell and Bee, 2014).…”

“…Perhaps for this reason, rhesus monkeys (Macaca mulatta) preferentially orient their heads to the right side when conspecific calls are presented from a position directly behind the subjects, while turning to the left when presented with interspecific sounds (Hauser and Andersson, 1994). The same head orientation task has been conducted on sea lions (Zalophus californianus) (Böye et al, 2005), horses (Equus caballus) (Basile et al, 2009) and dogs (Canis familiaris) (Reinholz-Trojan et al, 2012;Siniscalchi et al, 2008), yielding results comparable to those obtained with rhesus monkeys.…”

Lateralized Functions in the Dog Brain

“…In a similar way to what has been previously reported about vision, in this experimental condition, left-head orienting turns also led to longer latencies to resume feeding from the bowl. On the other hand, dogs consistently turned the head with their right ear leading in response to playbacks of canine vocalizations ("disturbance" and "isolation" calls) supporting the role of the left hemisphere in the analysis of familiar conspecific calls, as reported in other species (non-human primates [23], horses [24], cats [25] and sea lions [26]). Nevertheless, in dogs, conspecific vocalizations are not always processed by the left hemisphere, since the right hemisphere is used for processing vocalizations when they elicit intense emotion [6,7].…”