Abstract: Despite the abundant empirical evidence on lateralized social behaviours, a clear understanding of the relative roles of two brain hemispheres in social processing is still lacking. This study investigated visual lateralization in social interactions of free-ranging European bison (Bison bonasus). The bison were more likely to display aggressive responses (such as fight and side hit), when they viewed the conspecific with the right visual field, implicating the left brain hemisphere. In contrast, the responses associated with positive social interactions (female-to-calf bonding, calf-to-female approach, suckling) or aggression inhibition (fight termination) occurred more likely when the left visual field was in use, indicating the right hemisphere advantage. The results do not support either assumptions of right-hemisphere dominance for control of various social functions or hypotheses about simple positive (approach) versus negative (withdrawal) distinction between the hemispheric roles. The discrepancy between the studies suggests that in animals, the relative roles of the hemispheres in social processing may be determined by a fine balance of emotions and motivations associated with the particular social reaction difficult to categorize for a human investigator. Our findings highlight the involvement of both brain hemispheres in the control of social behaviour.

Abstract: Laterality in horses has been studied in recent decades. Although most horses are kept for riding purposes, there has been almost no research on how laterality may be affected by carrying a rider. In this study, 23 horses were tested for lateral preferences, both with and without a rider, in three different experiments. The rider gave minimal aids and rode on a long rein to allow the horse free choice. Firstly, motor laterality was assessed by observing forelimb preference when stepping over a pole. Secondly, sensory laterality was assessed by observing perceptual side preferences when the horse was confronted with (a) an unfamiliar person or (b) a novel object. After applying a generalised linear model, this preliminary study found that a rider increased the strength of motor laterality (p = 0.01) but did not affect sensory laterality (p = 0.8). This suggests that carrying a rider who is as passive as possible does not have an adverse effect on a horse�s stress levels and mental state.

Abstract: Lateralization of the brain appeared early in evolution and many of its features appear to have been retained, possibly even in humans. We now have a considerable amount of information on the different forms of lateralization in a number of species, and the commonalities of these are discussed, but there has been relatively little investigation of the advantages of being lateralized. This article reports new findings on the differences between lateralized and nonlateralized chicks. The lateralized chicks were exposed to light for 24 h on day 19 of incubation, a treatment known to lead to lateralization of a number of visually guided responses, and the nonlateralized chicks were incubated in the dark. When they were feeding, the lateralized chicks were found to detect a stimulus resembling a raptor with shorter latency than nonlateralized chicks. This difference was not a nonspecific effect caused by the light-exposed chicks being more distressed by the stimulus. Instead, it appears to be a genuine advantage conferred by having a lateralized brain. It is suggested that having a lateralized brain allows dual attention to the tasks of feeding (right eye and left hemisphere) and vigilance for predators (left eye and right hemisphere). Nonlateralized chicks appear to perform these dual tasks less efficiently than lateralized ones. Reference is made to other species in discussing these results.

Abstract: Idiosyncratic motor behaviour was investigated during four experimental procedures in 40 horses (males = 20, females = 20) to establish if horses revealed evidence of significant right or left laterality. The experimental procedures included (1) detection of the preferred foreleg to initiate movement (walk or trot), (2) obstacle avoidance within a passageway (right or left), (3) obstacle avoidance when ridden and (4) idiosyncratic motor bias when rolling. The influence of the horses' sex on both the direction and the degree of the laterality was explored within and between experimental procedures. The findings showed that the direction, but not the degree of idiosyncratic motor preference in the horses was strongly sex-related. Male horses exhibited significantly more (t = 3.74, d.f. = 79, P < 0.001) left lateralised responses and female horses exhibited significantly more (t = -6.35, d.f. = 79, P < 0.01) right lateralised responses. There was also significant positive correlation (P < 0.05) between four of six possible inter-experimental relationships. The results suggest two discrete trends of laterality associated with the sex of the horse. The primary cause of idiosyncratic motor laterality may be genetically predetermined, influenced by environmental factors or a combination of these two and the current findings may support the development of sex-specific training schedules for the horse. Further, work in this area might assist in defining the mechanisms of brain hemisphere lateralisation and allocation of cognitive function in the horse.

Abstract: Over the past 2 decades, numerous studies have been undertaken to assess motor laterality in the domestic dog. In anticipation of growth in this area of enquiry, we decided to review the literature on canine motor biases to identify any shortcomings, reflect on the lessons to be learned from and offer ways forward for future research into canine laterality. The aim of this review is to (i) summarize motor laterality findings in the dog, (ii) highlight areas lacking in standardization, and (iii) propose necessary criteria for future tests and global reporting protocols. Our review of the literature highlighted the lack of standardization between studies in task selection, sample size, number of behavior scores recorded, and the methods by which motor laterality were classified and reported. This review illustrates the benefits of standardizing methods of motor laterality assessment so that comparisons can be made between the populations sampled. By adopting such an approach, researchers should mutually benefit as motor laterality data could then be compared and subjected to meta-analysis.