A novel task to assess mood congruent memory bias in non-human animals

Trait sensitivity to stress and cognitive bias processes in fish: A brief overview

Like other animals, fish have unique personalities that can affect their cognition and responses to environmental stressors. These individual personality differences are often referred to as "behavioural syndromes" or "stress coping styles" and can include personality traits such as boldness, shyness, aggression, exploration, locomotor activity, and sociability. For example, bolder or proactive fish may be more likely to take risks and present lower hypothalamo-pituitary-adrenal/interrenal axis reactivity as compared to shy or reactive individuals. Likewise, learning and memory differ between fish personalities. Reactive or shy individuals tend to have faster learning and better association recall with aversive stimuli, while proactive or bold individuals tend to learn more quickly when presented with appetitive incentives. However, the influence of personality on cognitive processes other than cognitive achievement in fish has been scarcely explored. Cognitive bias tests have been employed to investigate the interplay between emotion and cognition in both humans and animals. Fish present cognitive bias processes (CBP) in which fish's interpretation of stimuli could be influenced by its current emotional state and open to environmental modulation. However, no study in fish has explored whether CBP, like in other species, can be interpreted as long-lasting traits and whether other individual characteristics may explain its variation. We hold the perspective that CBP could serve as a vulnerability factor for the onset, persistence, and recurrence of stress-related disorders. Therefore, studying fish's CBP as a state or trait and its interactions with individual variations may be valuable in future efforts to enhance our understanding of anxiety and stress neurobiology in animal models and humans.

How to Understand Them? A Review of Emotional Indicators in Horses

Stabled horses often experience negative emotions due to the inappropriate living conditions imposed by humans. However, identifying what emotions horses experience and what can trigger positive and negative emotions in stabled horses can be challenging. In this article we present a brief history of the study of emotions and models that explain emotions from a scientific point of view and the physiological bases and functions of emotions. We then review and discuss physiological and behavioral indicators and cognitive bias tests developed to assess emotions in horses. Hormone concentrations, body temperature, the position of the ears, facial expressions and behaviors, such as approach and avoidance behaviors, can provide valuable information about emotional states in horses. The cognitive bias paradigm is a recent and robust tool to assess emotions in horses. Knowing how to evaluate the intensity and frequency of an individual's emotions can guide horse owners and caretakers to identify practices and activities that should be stimulated, avoided or even banned from the individual's life, in favor of a life worth living. The development and validation of novel indicators of emotions considering positive and negative contexts can help in these actions.

Changes in group behaviour in response to a preferred environment reflect positive affect

When observed in their preferred environments, animals display behavioural changes, such as an increase in resting or a reduction in agonism, suggestive of positive affect and improved welfare. However, most studies focus on the behaviour of individuals or, at most, pairs of animals; even though in group-living animals beneficial environmental changes may impact on how the group behaves as a whole. In this study, we investigated whether experiencing a preferred visual environment affected the shoaling behaviour of zebrafish (Danio rerio) groups. We first confirmed a group preference for an image of gravel placed underneath the base of a tank compared to a plain white image. Second, we observed replicated groups either with or without the preferred (gravel) image present to determine if a visually enriched and preferred environment could elicit changes in shoaling behaviour. We found a significant interaction between the observation time and test condition, with differences in shoaling behaviour reflective of increased relaxation emerging gradually over time in the gravel condition. The findings of this study reveal that experiencing a preferred environment can alter group behaviour, making such holistic changes valuable as potential indicators of positive welfare.

Is there a bias in spatial maze judgment bias tests? Individual differences in subjects' novelty response can affect test results

Judgment bias tests have become an important tool in the assessment of animals' affective states. Subjects are first trained to discriminate between two cues associated with a positive and a less-positive outcome. After successful training, they are confronted with an ambiguous cue, and responses are used for judgment bias assessment. In spatial settings, ambiguous cue presentation is typically linked with novelty, i.e. to yet unexplored areas or areas to which the animal has a low degree of habituation. We hypothesized that in such settings, responses to ambiguity might be biased by the animals' perception of novelty. We conducted judgment bias tests in mound-building mice phenotyped for their exploration tendency. After subjects had learned to distinguish between the positively and less-positively rewarded arms of a maze, a new ambiguous middle-arm was introduced. During the first test trial, more exploratory, less neophobic individuals displayed higher bidirectional locomotion in the ambiguous arm, indicating intensive exploration. Although this resulted in longer latencies to the reward in more exploratory animals, we conclude that this did not reflect a 'more pessimistic judgment of ambiguity'. Indeed, during the following two trials, with increasing habituation to the ambiguous arm, the direction of the association was inversed compared to the first trial, as more exploratory individuals showed relatively shorter approach latencies. We suggest that in spatial test settings associating the ambiguous cue to novel areas, results can be confounded by subjects' personality-dependent motivational conflict between exploration and reaching the reward. Findings obtained under such conditions should be interpreted with care.

Optimism, pessimism and judgement bias in animals: A systematic review and meta-analysis

Just as happy people see the proverbial glass as half-full, 'optimistic' or 'pessimistic' responses to ambiguity might also reflect affective states in animals. Judgement bias tests, designed to measure these responses, are an increasingly popular way of assessing animal affect and there is now a substantial, but heterogeneous, literature on their use across different species, affect manipulations, and study designs. By conducting a systematic review and meta-analysis of 459 effect sizes from 71 studies of non-pharmacological affect manipulations on 22 non-human species, we show that animals in relatively better conditions, assumed to generate more positive affect, show more 'optimistic' judgements of ambiguity than those in relatively worse conditions. Overall effects are small when considering responses to all cues, but become more pronounced when non-ambiguous training cues are excluded from analyses or when focusing only on the most divergent responses between treatment groups. Task type (go/no-go; go/go active choice), training cue reinforcement (reward-punishment; reward-null; reward-reward) and sex of animals emerge as potential moderators of effect sizes in judgement bias tests.

Where Do We Stand in the Domestic Dog ( Canis familiaris ) Positive-Emotion Assessment: A State-of-the-Art Review and Future Directions

Although there have been a growing number of studies focusing on dog welfare, the research field concerning dog positive-emotion assessment remains mostly unexplored. This paper aims to provide a state-of-the-art review and summary of the scattered and disperse research on dog positive-emotion assessment. The review notably details the current advancement in dog positive-emotion research, what approaches, measures, methods, and techniques have been implemented so far in emotion perception, processing, and response assessment. Moreover, we propose possible future research directions for short-term emotion as well as longer-term emotional states assessment in dogs. The review ends by identifying and addressing some methodological limitations and by pointing out further methodological research needs.

Use of cognitive bias as a welfare tool in poultry

In human psychology, the link between cognition and emotions is broadly accepted. However, the idea of using the interaction between cognition and emotions as a tool for a better understanding of animal emotions or for welfare assessment is relatively new. The first avian species used in cognitive bias tests was the European starling followed by the domestic chicken and other species. The most frequently used paradigm is the affect-induced judgment bias. There are many variations of the judgment bias tests in birds. The test itself is preceded by discrimination training. Discrimination tasks vary from visual cue discrimination, discrimination of time intervals to spatial location discrimination. During the discrimination training, birds flip or do not flip the lids of the food dishes, and their latency to approach the cues in a straight alley maze, in a two-choice arena, or different locations in spatial judgment task arena are measured. Alternately, the birds fulfill operant tasks in a Skinner box. Before or after the discrimination training phase, birds are subjected to manipulations that are hypothesized to induce positive or negative emotional states. In the last stage, birds are subjected to judgment bias tests. The assumption is that animals in a negative affective state would more likely respond to ambiguous cues, as if they predict the negative event, than animals in a more positive state. However, the results of some avian studies are inconsistent, particularly those studying the effect of environmental enrichment. In starlings, each of the three studies has supplied conflicting results. In poultry, none of the four studies demonstrated a positive effect of environmental enrichment on emotional states. Only the study using unpredictable stressors in combination with environmental complexity showed that animals kept in a more complex environment are more optimistic. Manipulation of the social environment seems to be more effective in judgment bias induction. Conflicting results could be attributable to the design of the tests, the manner of affect induction, or the data analysis. Further optimization and validation of avian cognitive bias tests could help to avoid problems such as the loss of ambiguity. New methods of attention and memory bias testing are promising. However, regardless of the abovementioned complications, a cognitive bias paradigm is a valuable tool, which can help us better understand avian emotions and assess poultry welfare.

Social proximity in dairy calves is affected by differences in pessimism

Negative social interactions have been extensively studied in dairy cattle, but little is known about the establishment of positive (preferential) relationships. Adult dairy cows are known to spend more time at close proximity to specific social partners, indicating that they establish stronger bonds with these animals, but few studies have explored what happens in socially housed calves. In this study, we explored whether calves that spent their entire life in the same social group established social preferences (i.e. pairs of individuals that interact more) that are stable over time (two 48-h periods, separated by three days), across two types of behavior (standing and lying) and across contexts (change in environment and housing design). When housed in an open pack, calves showed consistent proximity patterns when standing (but not when lying). These preferential relationships persisted even after calves were moved into a new pen fitted with free stalls. At the individual level, calves varied in how selective they were in their social relationships, with some calves spending much more time with specific partners than did others. This degree of selectivity was not associated to Sociability, marginally associated to Fearfulness, but was associated with Pessimism (more pessimistic calves were more selective in their social relationships). In conclusion, calves can form selective relationships that appeared to be consistent over time and across context, and the degree to which calves were selective varied in relation to individual differences in Pessimism.

Symposium review: Scientific assessment of affective states in dairy cattle

Affective states, which refer to feelings or emotions, are a key component of animal welfare, but these are also difficult to assess. Drawing upon a body of theoretical and applied work, we critically review the scientific literature on the assessment of affective states in animals, drawing examples where possible from research on dairy cattle, and highlighting the strengths and weaknesses of scientific methods used to assess affective states in animals. We adopt the "valence/arousal" framework, describing affect as a 2-dimensional space (with valence referring to whether an experience is positive or negative, and arousal referring to the intensity of the experience). We conclude that spontaneous physiological and behavioral responses typically reflect arousal, whereas learned responses can be valuable when investigating valence. We also conclude that the assessment of affective states can be furthered using mood assessments and that the use of drug treatments with known emotional effects in humans can be helpful in the assessment of specific affective states in animals.

Pair-bonding influences affective state in a monogamous fish species

In humans, affective states are a key component in pair-bonding, particularly in the early stage of a relationship. Pairing with a high-quality partner elicits positive affective states which, in turn, validate and reinforce the mate choice. Affective states thus strongly affect pair stability and future reproductive success. We propose generalizing the link between affective states and pair-bonding to encompass other monogamous species exhibiting biparental care, chiefly where the reproductive success of the pair critically depends on the coordination between partners. The convict cichlid Amatitlania siquia is a monogamous fish species that forms long-lasting pairs with strong cooperation between parents for parental care. In this species, we showed that females paired with their non-preferred male had lower reproductive success than those paired with their preferred male. We then transposed the judgement bias paradigm, previously used in other animal species, to assess objectively affective states in fishes. Females that were assigned their non-preferred partner exhibited pessimistic bias, which indicates a negative affective state. By contrast, females that were assigned their preferred partner did not exhibit changes in their affective state. Our results highlight that the influence of pair-bonding on affective states is not human-specific and can also be observed in non-human species.