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Rogers, L. J. (2000). Evolution of hemispheric specialization: advantages and disadvantages. Brain Lang, 73(2), 236–253.
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.
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McGreevy, P. D., & Rogers, L. J. (2005). Motor and sensory laterality in thoroughbred horses. Appl. Anim. Behav. Sci., 92(4), 337–352.
Abstract: We investigated lateralisation in horses because it is likely to be important in training and athletic performance. Thoroughbred horses (n = 106) were observed every 60 s for 2 h, when they were at pasture, and the position of the forelimbs in relation to one another was recorded. There was a population bias skewed to standing with the left forelimb advanced over the right (i.e. directional lateralisation). Using the first 50 observations, the distribution of preferences was 43 significantly left, 10 significantly right with 53 being non-significant (i.e. ambidextextrous). The strength of motor bias increased with age, suggesting maturation or an influence of training. The horses were also presented with an olfactory stimulus (stallion faeces) to score the tendency to use one nostril rather than the other. A significant preference to use the right nostril first was shown in horses under 4 years of age (n = 61) but not in older horses. Of the 157 horses tested for nostril bias, 76 had been assessed for motor bias and so were used for analysis of the relationship between laterality in the two modalities. There was no significant relationship between direction of foreleg motor bias and first nostril used, total number of inhalations or laterality index of nostril use. The absence of a correlation between laterality of nostril use and motor bias indicates that lateralisation of the equine brain occurs on at least two levels of neural organisation--sensory and motor--a finding that is consistent with other examples of lateralisation in species that have been examined in more detail.
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Rogers, L. J. (2010). Relevance of brain and behavioural lateralization to animal welfare. Appl. Anim. Behav. Sci., 127(1-2), 1–11.
Abstract: The left and right sides of the brain are specialised to process information in different ways and to control different categories of behaviour. Research on a range of species has shown that the left hemisphere controls well-established patterns of behaviour performed in non-stressful situations, whereas the right hemisphere responds to unexpected stimuli and controls escape and other emergency responses. The known functions of each hemisphere are summarised in this paper. Then it is hypothesised that stressed animals rely on predominant use of the right hemisphere, and that a bias to use the right or left hemisphere, respectively, may explain the behavioural differences between animals with a negative cognitive bias and those with a positive cognitive bias. In some species of primates it has been shown that the preferred limb used to pick up food when the animal is in a relaxed state reflects the dominant hemisphere and may be an accessible measure indicating susceptibility to stress and tendency towards positive versus negative cognitive bias. Hence, limb preference might be a useful measure of such tendencies in domesticated species. Some difficulties in determining a relevant measure of limb preference in non-primate species are mentioned, followed by the suggestion that eye preferences for viewing certain stimuli may be a useful measure in species with laterally placed eyes. Finally, effects of experience on the development of hemispheric dominance are discussed, leading to a suggestion that the welfare of domestic animals may be enhanced by ensuring development of left hemisphere dominance (e.g. by exposing chick embryos to light) and by shifting right to left hemisphere dominance in animals with negative cognitive bias.
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Austin, N. P., & Rogers, L. J. (2014). Lateralization of agonistic and vigilance responses in Przewalski horses (Equus przewalskii). Applied Animal Behaviour Science, 151, 43–50.
Abstract: tEye and limb preferences were scored in the closest undomesticated relative of Equuscaballus using the same methods as used previously to study laterality in feral horses.Observations were made of 33 Przewalski horses (Equus ferus przewalskii) (male N = 20,female N = 13) living under natural social conditions on a large reserve in France. Signifi-cant left-eye/side biases were found in agonistic interactions within harem bands (M ± SEbias to left 58% ± 0.01 for threats, P < 0.001; 68% ± 0.05 for attacks; P < 0.001) and in stallionfights (threats, 52% ± 0.01 left, P < 0.001; attacks, 63% ± 0.02 left, P < 0.001): as many as 80%of the horses were significantly lateralized in attack responses within harem bands. Lat-erality of vigilance was measured as lifting up the head from grazing and turning it to theleft or right side: a directional bias to the left was found (M ± SE 53% ± 0.02 left, P < 0.001).Side bias in reactivity was calculated as the percent of head lifts above the level of thewithers on the left or right side and this was also left side biased (M ± SE 73% ± 0.03 left,P < 0.001). These results indicate right-hemisphere specialization for control of aggressionand responses to novelty. The left bias in attack scores within harem bands was strongerin males than females (P = 0.024) and in immature than adult horses (P = 0.032). Immaturehorses were also more strongly lateralized than adults in vigilance scores (P = 0.022), whichmay suggest that experience reduces these side biases. Our results show that Przewalskihorses exhibit left eye preferences, as do feral horses, and do so even more strongly thanferal horses. Considering feral and Przewalski horses together, we deduce that ancestralhorses had similar lateral biases. Also similar to feral horses, the Przewalski horses showedno significant forelimb preference at the group level or in the majority of horses at theindividual level, confirming the hypothesis that previously reported limb preferences indomestic breeds are entrained or generated by breed-specific selection.
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Robins, A., & Rogers, L. J. (2004). Lateralized prey-catching responses in the cane toad, Bufo marinus: analysis of complex visual stimuli. Anim. Behav., 68(4), 767–775.
Abstract: We tested the responses of Bufo marinus to prey stimuli of varying visual complexity that were moved around the toads in either a clockwise or anticlockwise direction at 1.7 revolutions/min. Predatory responses directed at prey resembling an insect were frequent when the model insect moved clockwise across the visual midline into the right visual hemifield. In contrast, the toads tended to ignore such stimuli when they moved anticlockwise across the midline into the left hemifield. No such lateralization was found when a rectangular strip moved along its longest axis was presented in a similar way. The toads also directed more responses towards the latter stimulus than towards the insect prey. Hence, the results suggest that lateralized predatory responses occur for considered decisions on whether or not to respond to complex insect-like stimuli, but not for decisions on comparatively simple stimuli. We discuss similarities between the lateralized feeding responses of B. marinus and those of avian species, as support for the hypothesis that lateralized brain function in tetrapods may have arisen from a common lateralized ancestor.
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Austin, N. P., & Rogers, L. J. (2012). Limb preferences and lateralization of aggression, reactivity and vigilance in feral horses, Equus caballus. Anim. Behav., 83(1), 239–247.
Abstract: Observational field studies were conducted on two remote populations of feral horses in Australia to determine whether lateralization is a characteristic of Equus caballus as a species or results from handling by humans. Group 1 had been feral for two to five generations and Group 2 for 10–20 generations. In both groups, left-side biases were present during agonistic interactions and in reactivity and vigilance. Therefore, as in other vertebrates, the right hemisphere appears to be specialized to control agonistic behaviour and responses to potential threats. The leftwards bias was stronger in measures of behaviour involving more aggression and reactivity. Preferences to place one forelimb in front of the other during grazing were also determined. No population bias of forelimb preference was found, suggesting that such limb preferences present in domestic horses may be entrained. Since stronger individual limb preferences were found in immature than in adult feral horses, limb preference may be modified by maturation or experience in the natural habitat. Stronger limb preference was associated significantly with elevated attention to the environment but only in younger feral horses. No sex differences in lateralization were found. The findings are evidence that horses show visual lateralization, as in other vertebrates, not dependent on handling by humans. Limb preference during grazing, by contrast, does appear to depend on experience.
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Rogers, L. J. (2002). Advantages and disadvantages of lateralization. In L. J. Rogers, & R. Andrew (Eds.), (pp. 126–153). New York: Cambridge University Press.
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