Visual lateralization in wild striped dolphins (Stenella coeruleoalba) in response to stimuli with different degrees of familiarity

Mainly Visual Aspects of Emotional Laterality in Cognitively Developed and Highly Social Mammals-A Systematic Review

Several studies have shown that emotions are asymmetrically represented in the human brain and have proposed three main models (the 'right hemisphere hypothesis', the 'approach-withdrawal hypothesis' and the 'valence hypothesis') that give different accounts of this emotional laterality. Furthermore, in recent years, many investigations have suggested that a similar emotional laterality may also exist in different animal taxa. However, results of a previous systematic review of emotional laterality in non-human primates have shown that some of these studies might be criticized from the methodological point of view and support only in part the hypothesis of a continuum in emotional laterality across vertebrates. The aim of the present review therefore consisted in trying to expand this survey to other cognitively developed and highly social mammals, focusing attention on mainly visual aspects of emotional laterality, in studies conducted on the animal categories of horses, elephants, dolphins and whales. The 35 studies included in the review took into account three aspects of mainly visual emotional laterality, namely: (a) visual asymmetries for positive/familiar vs. negative/novel stimuli; (b) lateral position preference in mother-offspring or other affiliative interactions; (c) lateral position preference in antagonistic interactions. In agreement with data obtained from human studies that have evaluated comprehension or expression of emotions at the facial or vocal level, these results suggest that a general but graded right-hemisphere prevalence in the processing of emotions can be found at the visual level in cognitively developed non-primate social mammals. Some methodological problems and some implications of these results for human psychopathology are briefly discussed.

Left or right, that is the question: use of egocentric frame of reference and the right-eye advantage for understanding gestural signs in bottlenose dolphins (Tursiops truncatus)

How do bottlenose dolphins visually perceive the space around them? In particular, what cues do they use as a frame of reference for left-right perception? To address this question, we examined the dolphin's responses to various manipulations of the spatial relationship between the dolphin and the trainer by using gestural signs for actions given by the trainer, which have different meanings in the left and right hands. When the dolphins were tested with their backs to the trainer (Experiment 1) or in an inverted position underwater (Experiments 2 and 3), correct responses from the trainer's perspective were maintained for signs related to movement direction instructions. In contrast, reversed responses were frequently observed for signs that required different sounds for the left and right hands. When the movement direction instructions were presented with symmetrical graphic signs such as " × " and "●", accuracy decreased in the inverted posture (Experiment 3). Furthermore, when the signs for sounds were presented from either the left or right side of the dolphin's body, performance was better when the side of the sign movement coincided with the body side on which it was presented than when it was mismatched (Experiment 4). In the final experiment, when one eye was covered with an eyecup, the results showed that, as in the case of body-side presentation, performance was better when the open eye coincided with the side on which the sign movement was presented. These results indicate that dolphins used the egocentric frame for visuospatial cognition. In addition, they showed better performances when the gestural signs were presented to the right eye, suggesting the possibility of a left-hemispheric advantage in the dolphin's visuospatial cognition.

Cetacean responses to violation of expectation paradigm in a free-swim context

The investigation of individual responses to unexpected stimuli or outcomes provides insights into basic cognitive processes, such as mental representations, emotional states of surprise, and detections of anomalies. Three experiments using a violation of expectation paradigm were conducted with 12 belugas and 17 bottlenose dolphins in managed care to test two classes of stimuli (humans and objects) in manipulated sequences of familiar and unfamiliar humans (Study 1, trainers and strangers), familiar and unfamiliar objects (Study 2, typical enrichment devices and new objects), and finally objects and humans (Study 3). Gaze durations were assessed for each condition in a given study during free-swim contexts. The results supported previous findings that visual stimuli, regardless of class, were stimulating and intriguing for both belugas and bottlenose dolphins. Belugas were more likely to gaze longer at human and object stimuli and tended to gaze longer at unexpected experiences than control or expected experiences. Bottlenose dolphins showed similar trends except when objects were involved. Individual variability was present for both species with some individuals showing stronger patterns of responses for expected experiences than others. After 2 years of intermittent experiments, belugas and bottlenose dolphins in managed care maintained their curiosity about visual stimuli, for which they received no primary reinforcement. Investigating responses to unexpected stimuli with animals in managed care may provide insight into how these animals respond to biologically relevant conditions, such as boat presence, predators, and unfamiliar conspecifics.

Cognition of the manatee: past research and future developments

In this paper, we present a review of the current knowledge related to the cognitive abilities of the manatee, with a focus on the Antillean manatee in situ and ex situ. Following a biocentric approach, we consider the animals' ecology, perception and sociality and we introduce future perspectives on their cognition. Scientific literature on the cognitive abilities of Antillean manatees' is limited and mainly linked to medical training and veterinary manipulations. To perceive and to interact with their social and natural environment (e.g. social interactions, foraging and traveling), manatees use visual, acoustic and tactile modalities that may be involved in a large range of cognitive abilities. Research on stimuli perception in manatees is scarce; however, these animals demonstrate abilities to learn and appear to show long-term memory. For example, to mate and/or to forage manatees travel at medium and large geographical scales; without doubt their movements entail the use of a set of stimuli and learning processes. Furthermore, their social skills (e.g. social organization, tactile and acoustic communications) are also poorly understood although their social interactions appear to be more complex than previously thought. Finally, as for many animals, temperament/personality may play a key role during their interactions with conspecifics and the environment. These aspects on manatee behavior and cognition are important for management and conservation purposes and help us understand the evolution of these marine mammals.

Bottlenose dolphins' (Tursiops Truncatus) visual and motor laterality depending on emotional contexts

Hemispheric lateralization is a specialized neural and cognitive processing achieved preferentially by either the left or the right hemisphere of the brain. Among vertebrates, emotions processing seems to be lateralized, but the involvement of each hemisphere is still on debate. Our study investigated visual and motor laterality on five bottlenose dolphins' (Tursiops truncatus) during spontaneous and experimentally induced emotional contexts. We measured motor laterality in pectoral used and swimming position during positive social interactions. Additionally, during training sessions, stimuli with positive or negative emotional valences were presented either on the dolphins' left or right side. Emotional reactions toward stimuli were measured and a visual laterality index was calculated. Dolphins were visually left-lateralized during training sessions. They also reacted more when negative stimuli were presented on their left side than right side during the first stimuli presentation. Our results suggest that bottlenose dolphins, like other vertebrates, may present a right hemisphere dominance for social information processing, detection of and response to unpredictable or novel stimuli and a left-hemisphere dominance during escape responses inhibition. Further studies on a larger sample size should explore inter-individual variation and identify other potential contexts in which lateralization emerges. Emotional lateralization should be considered as a potential indicator for future dolphin welfare assessment.

When perceptual laterality vanishes with curiosity: A study in dolphins and starlings

Sensory laterality is influenced by the individual's attentional state. There are variations in the way different individuals of a same species attend to stimuli. When confronted to novelty, some individuals are more explorative than others. Curiosity is composed of sensation and knowledge seeking in humans. In the present study, we hypothesized that more curious animals, i.e., showing more sensory exploration would be less lateralized than quietly attentive individuals, performing instead more gazing behaviours. In order to test this hypothesis and its possible generality, we performed two studies using two animal models (dolphins and starlings) and two modalities (visual and auditory) of presentation of species-specific and non-species-specific stimuli. Both dolphins and starlings presented more gazes for the species-specific stimuli and more exploratory components for the non-species-specific stimuli. Moreover, in both cases, the non-species-specific stimuli involved more lateralized responses whereas there was no or less clear laterality for the species-specific stimuli. The more exploratory dolphins and starlings also showed a decreased laterality: the more "curious" individuals showed no laterality. Further studies are needed on characterization of curiosity in relation to attention structure. The present study suggests that individual variations in sensory laterality may help disentangle the subtle differences between curiosity, attention and boldness.

Visual lateralization in artiodactyls: A brief summary of research and new evidence on saiga antelope

The visual system and lifestyle characteristics make the even-toed ungulates an excellent model for the studies of behavioural lateralization. Recent research has focused on these mammals providing evidence of lateralization in a wide range of behaviours. This provides an opportunity for the collation of the current theoretical assumptions and the existing empirical evidence for visual lateralization in artiodactyls. In the present study, we aim first to gain a fuller picture of hemispheric specializations in saiga antelopes by investigating the lateralization of vigilance and novel object inspection in the wild. Second, we summarized the results of the research into visual lateralization in even-toed ungulates and attempted to assess the applicability of two popular hypotheses about the division of hemispheric roles. The results on saigas show a significant preference for head turns to the right visual field during vigilance which was more robust in individuals in larger groups. When an unfamiliar artificial object was placed in their natural setting, saigas preferentially viewed it predominantly with the right eye. These results, together with the cumulative evidence in artiodactyls, do not follow either the approach-withdrawal or positivity-negativity dichotomous patterns widely used to explain the division of functions between the hemispheres.

Do dolphins really have a rightward lateralization for action? The importance of behavior-specific and orientation-neutral coding

Because each side of the vertebrate body is controlled by a different side of the brain, studies of behavioral lateralization can provide insight into functional cerebral asymmetries in humans and other animals. The current study examined behavioral lateralization for a variety of behaviors in a group of 26 dolphins, in order to assess the claim that cetaceans show strong rightward action asymmetries indicative of a left-hemisphere specialization for action. We distinguished between side asymmetries and whole body turning actions, and devised a new coding system to counter the problem that previous studies of rolling behaviors (i.e., rotations around the long axis) have used contradictory coding systems depending on species' typical orientation. Our results did not support a generalized population-level rightward action asymmetry across multiple behaviors. Instead, we suggest that many dolphin behavioral asymmetries may be better explained as a result of perceptual processing asymmetries common across many vertebrates.

Behavioural laterality in foraging bottlenose dolphins (Tursiops truncatus)

Lateralized behaviour is found in humans and a wide variety of other species. At a population level, lateralization of behaviour suggests hemispheric specialization may underlie this behaviour. As in other cetaceans, dolphins exhibit a strong right-side bias in foraging behaviour. Common bottlenose dolphins in The Bahamas use a foraging technique termed 'crater feeding', in which they swim slowly along the ocean floor, scanning the substrate using echolocation, and then bury their rostrums into the sand to obtain prey. The bottlenose dolphins off Bimini, The Bahamas, frequently execute a sharp turn before burying their rostrums in the sand. Based on data collected from 2012 to 2018, we report a significant right-side (left turn) bias in these dolphins. Out of 709 turns recorded from at least 27 different individuals, 99.44% (n = 705) were to the left (right side and right eye down) [z = 3.275, p = 0.001]. Only one individual turned right (left side and left eye down, 4/4 turns). We hypothesize that this right-side bias may be due in part to the possible laterization of echolocation production mechanisms, the dolphins' use of the right set of phonic lips to produce echolocation clicks, and a right eye (left hemisphere) advantage in visual discrimination and visuospatial processing.

Lateralization in accuracy, reaction time and behavioral processes in a visual discrimination task in an Indo-Pacific bottlenose dolphin (Tursiops aduncus)

Perceptual and behavioral asymmetry has been observed in a wide range of vertebrate and invertebrate species with its origin estimated to go back over 500 million years. Previously, hemispheric lateralization in marine mammals has been recorded during foraging, parental care, preferred swimming direction as well as when solving cognitive challenges. Visual laterality has been demonstrated in preferred eye use and performance accuracy. A female Indo-Pacific bottlenose dolphin was trained to associate eight pairs of non-identical visual stimuli. Her performance was tested and compared under binocular and monocular conditions. No significant difference was found in accuracy, while a clear left eye advantage was demonstrated in reaction time. In addition, behavioral asymmetry was observed in movement pattern preference during the stimulus discrimination.

Affect-Driven Attention Biases as Animal Welfare Indicators: Review and Methods

Attention bias describes the differential allocation of attention towards one stimulus compared to others. In humans, this bias can be mediated by the observer's affective state and is implicated in the onset and maintenance of affective disorders such as anxiety. Affect-driven attention biases (ADABs) have also been identified in a few other species. Here, we review the literature on ADABs in animals and discuss their utility as welfare indicators. Despite a limited research effort, several studies have found that negative affective states modulate attention to negative (i.e., threatening) cues. ADABs influenced by positive-valence states have also been documented in animals. We discuss methods for measuring ADAB and conclude that looking time, dot-probe, and emotional spatial cueing paradigms are particularly promising. Research is needed to test them with a wider range of species, investigate attentional scope as an indicator of affect, and explore the possible causative role of attention biases in determining animal wellbeing. Finally, we argue that ADABs might not be best-utilized as indicators of general valence, but instead to reveal specific emotions, motivations, aversions, and preferences. Paying attention to the human literature could facilitate these advances.

Mother and offspring lateralized social behavior across mammalian species

Findings on nonprimate mammals place the issue of mother-infant lateralized relations in a broader context, demonstrating that humans are one of many species showing this feature. The remarkable interspecies consistency in the direction of lateralization points to a continuity between lateralized mother-infant interactions in primates and nonprimate mammals and suggests ancient evolutionary roots of human cradling bias. The results from species which, in contrast to primates, have no direct involvement of forelimbs in mother-infant spatial interactions clearly support the perceptual origin of this type of lateralization. A right hemisphere advantage for social functions relevant to mother-infant interactions is the most probable background for the left-sided biases in the behavior of mothers and infants. Recent findings suggest the contribution of lateralized mother-infant interactions to biological fitness. Mother and infant both can gain advantage from keeping the other on the left side.

Lateralization of mother-infant interactions in wild horses

The manifestation of behavioural lateralization has been shown to be modified by environmental conditions, life experiences, and selective breeding. This study tests whether the lateralization recently found in feral domestic horse (Equus caballus) is evident in undomesticated horses. Mother-offspring interactions were investigated in Przewalski's horse (E. ferus przewalskii) living in their natural habitat in Mongolia. Lateral position preferences during mare-foal spontaneous reunions were used as a behavioural marker of visual lateralization. Preferences were separately assessed for foals' approaches to their mothers and mares' approaches to their foals. Preference to keep the mother in the visual field of the left eye was found in various types of foals' behaviour. In slow travelling, Przewalski's foals showed stronger preference for the left eye use than feral horse foals. Population-level left-eye bias was also found in mothers approaching their foals. Our results indicate right-hemispheric dominance for control of mother-offspring interactions in Przewalski's horses, similar to what has been reported for other mammals including humans. Benefits conferred by the lateralized social processing of and responding to social stimuli may explain that the left-lateralized social behaviour is a robust trait of equine behaviour, not modified by domestication or specific environmental conditions of the population.

Spontaneous approaches of divers by free-ranging orcas (Orcinus orca): age- and sex-differences in exploratory behaviours and visual laterality

Running comparative studies of laterality in mammals is a way to deepen our understanding of the evolution of the brain hemisphere functions. Studies on vision highlighted a possible task-sharing between hemispheres depending on the characteristics of the observers, the nature of the observed stimulus and the context of the observation, a phenomenon that could go beyond the monitoring of conspecifics. Cetaceans are predators that adapted to an aquatic habitat and display a clear crossing of fibers to the side of the brain opposite the eye of origin. Here, we analysed the interactions between humans and cetaceans when free-ranging orcas approach divers. Our study concentrated on the spontaneous exploratory behaviours of divers by orcas depending on their age and sex, and on the possible expression of a visual laterality. The results showed a significant preference for the use of the left eye but exclusively in adult females. Adult males had a more sustained attention than adult females, marked by a higher spatial proximity to divers, slower approaches and longer look durations. Adult females, probably more cautious, explored from the distance and more furtively. Our findings support a possible link between attentional/motivational states and visual laterality in mammals.

The hypothesis of neuronal interconnectivity as a function of brain size-a general organization principle of the human connectome

Twenty years ago, Ringo and colleagues proposed that maintaining absolute connectivity in larger compared with smaller brains is computationally inefficient due to increased conduction delays in transcallosal information transfer and expensive with respect to the brain mass needed to establish these additional connections. Therefore, they postulated that larger brains are relatively stronger connected intrahemispherically and smaller brains interhemispherically, resulting in stronger functional lateralization in larger brains. We investigated neuronal interconnections in 138 large and small human brains using diffusion tensor imaging-based fiber tractography. We found a significant interaction between brain size and the type of connectivity. Structural intrahemispheric connectivity is stronger in larger brains, whereas interhemispheric connectivity is only marginally increased in larger compared with smaller brains. Although brain size and gender are confounded, this effect is gender-independent. Additionally, the ratio of interhemispheric to intrahemispheric connectivity correlates inversely with brain size. The hypothesis of neuronal interconnectivity as a function of brain size might account for shorter and more symmetrical interhemispheric transfer times in women and for empirical evidence that visual and auditory processing are stronger lateralized in men. The hypothesis additionally shows that differences in interhemispheric and intrahemispheric connectivity are driven by brain size and not by gender, a finding contradicting a recently published study. Our findings are also compatible with the idea that the more asymmetric a region is, the smaller the density of interhemispheric connections, but the larger the density of intrahemispheric connections. The hypothesis represents an organization principle of the human connectome that might be applied also to non-human animals as suggested by our cross-species comparison.