Judgement Bias Test Research Articles

Behaviour of horses in a judgment bias test associated with positive or negative reinforcement

Moods can influence our judgment of ambiguous stimuli as positive or negative. Measuring judgment bias in animals is a promising method to objectively assess their emotional states. Our study aimed to develop a cognitive bias test in horses, in order to assess the effect of training using positive reinforcement (PR) or negative reinforcement (NR) on their emotional states. We trained 12 mares to discriminate between a rewarded and a non-rewarded location situated on each side of a paddock. The mares were then trained during five days to perform several exercises using PR (n=6) for one group, and NR (n=6) for the other (treatment). Finally, we compared the responses of the two groups to three ambiguous locations situated between the rewarded and non-rewarded locations (judgment bias test). During the training exercises, according to our predictions, behavioural measures suggested that NR mares experienced more negative emotions than PR mares. Surprisingly, the results of the judgment bias test suggest that NR mares were in a more optimistic mood compared to PR mares, despite previously experiencing more negative emotions during the treatment. NR mares could have been more motivated to obtain a food reward than PR mares, which had been rewarded throughout the treatment phase. Alternatively, NR mares could have developed optimistic bias triggered by release from the negative state experienced during treatment. This first attempt to test judgment bias in horses suggests that this is a promising method to measure horse mood. Knowledge about the effect of training methods on the mental health of domesticated animals can add a new dimension to animal welfare, in order to promote better ways to work with animals.

Are hungry sheep more pessimistic? The effects of food restriction on cognitive bias and the involvement of ghrelin in its regulation

Food restriction is considered to be a welfare issue in extensively reared animals. However, the effects of food restriction on the affective state, and its physiological regulation, are unknown. In Experiment 1, we aimed to assess the effects of increased plasma concentrations of acyl-ghrelin on judgement bias (an indicator of affective states) by fasting sheep for 24h or by ghrelin administration. In Experiment 2, we aimed to assess the effects of chronic food restriction on judgement bias and attention bias towards a food-related cue. For the judgement bias test, sheep were trained in an arena to approach a positive location cue associated with conspecifics and not approach a negative location cue associated with a dog. Three non-trained, non-reinforced ambiguous location cues were situated between the positive and negative locations. Attention bias towards a food-related cue was assessed by placing an empty food bucket against the wall of the arena halfway between the entry point and the positive location. In Experiment 1, sheep were divided into three treatments; 24h fast, ghrelin administration or control. Judgement bias, locomotor activity and plasma cortisol concentrations were assessed. The ghrelin treated group tended to express a more pessimistic bias compared to the control group (P<0.1), and plasma cortisol concentrations tended to be increased (P<0.1). In Experiment 2, sheep were subjected to a high feeding level (HF) or low feeding level (LF) for 7days. The LF group tended to show a more optimistic judgement bias (P<0.1). When the food-related cue was presented, LF ewes took longer to reach the positive location (P<0.001), spent longer with their head inside the bucket (P<0.001) and more time interacting with the bucket (P<0.01). This study provides preliminary evidence that food restriction alters judgement bias and attention bias towards a food-related cue which may indicate altered affective states of sheep.

Chronic stress induces pessimistic-like judgment and learning deficits in sheep

Chronic stress can be described as a long-term negative affective state induced by an accumulation of negative emotional experiences that alters an individual's interactions with the environment. In humans, chronic stress induces both persistent judgment biases and learning deficits. We investigated whether similar cognitive biases could occur in sheep. Twenty-four lambs were subjected to a chronic stress treatment for 9 weeks (exposure to various unpredictable, uncontrollable and aversive events regularly encountered in ordinary agricultural practices) and 24 other lambs were used as a control group. Before treatment all the lambs had been trained to approach or avoid a food bucket depending on its location. After treatment, the lambs were individually exposed to two tests: (i) a food bucket approach/avoidance test, by testing the response of lambs to ambiguous locations of the bucket, i.e. a judgment bias test, (ii) a learning test consisting of training on six consecutive days to distinguish between two visual stimuli differing in their color and shape (acquisition phase) and re-exposure to the test conditions 2 days after the end of the acquisition phase (recall phase). In the judgment bias test, treated lambs took longer to approach the ambiguous locations of the bucket. During the learning test, treated lambs had lower numbers of correct choices than control lambs in the acquisition and recall phase. Hence sheep experiencing repeated aversive events demonstrated pessimistic-like judgment biases and learning deficits. These may be useful measures to assess long-term emotional states in animals.

Cross sectional study comparing behavioural, cognitive and physiological indicators of welfare between short and long term kennelled domestic dogs

Affective states are an integral part of animal welfare but are difficult to assess using traditional welfare measurements. It has previously been shown that kennelled dogs commonly show indications of poor welfare. The aim of this study was to compare welfare of short-term (ST) and long-term (LT) kennel housed rehoming centre dogs using a range of indicators. Affective states were measured with a judgement bias test, assessing whether dogs had a relatively optimistic or pessimistic interpretation of ambiguous stimuli. Direct assessment of behaviour in three situations (undisturbed, stranger passing, stranger approaching) was conducted, and urinary cortisol:creatinine (C:C) levels measured for each dog. Finally, each dog’s main caretaker completed two short questionnaires: an objective indication of dogs’ behavioural responses to familiar people, unfamiliar people and other dogs, and a more subjective staff evaluation of behavioural characteristics and overall welfare. ST and LT dogs did not differ in the judgement bias or urinary cortisol levels, although cortisol:creatinine ratios were relatively high in both groups and very variable between individual animals (mean=22.2×10−6; S.D.=13.0×10−6). Directly observed behaviours in kennels were also similar between groups, apart from LT dogs showing more resting behaviour when undisturbed, likely due to familiarisation with kennel routines. Staff perceived the welfare of both groups to be similar, but LT dogs were perceived to play less with people, bark and growl more at strange dogs and play more with objects when with another dog. These may be reasons for failure of dogs to be homed, rather than consequences of long term kennelling. Overall, this study suggested large individual variation in measures of welfare and behaviour, but few differences between dogs housed for more than 6 months as compared to those housed for shorter periods. This may suggest that the welfare of dogs is influenced more by specific aspects of their individual kennel experience rather than the overall time spent in a kennel environment.

Brief owner absence does not induce negative judgement bias in pet dogs

Humans in a negative emotional state are more likely to judge ambiguous stimuli as negative. In recent years, similar judgement biases have been found in some non-human animals that were exposed to long-term or short-term treatments aimed at influencing their affective states. Here we tested pet dogs in the presence and absence of their owners in a judgement bias test with an established go/no-go procedure. Even though owner absence is thought to induce a state of anxiety in dogs that have formed an attachment bond with their primary caretakers, we found no difference between the dogs' responses to ambiguous stimuli in the presence or absence of their owners. This result may be explained by the absence of anxiety in dogs that are accustomed to brief periods of separation from their owners, or by a sensitivity limit of the customary judgement bias tests in non-human animals when only a moderate, short-term state of anxiety is induced. In addition, we found significant differences between individuals and populations in the responses to ambiguous stimuli, which give impetus for further research.

A test to identify judgement bias in mice

Emotional states are known to affect cognitive processes. For example highly anxious individuals interpret ambiguous stimuli more negatively than low anxious people, an effect called negative judgement bias. Recently, the measurement of judgement bias has been used to try and indicate emotional states in animals. In the present experiment a potential test for judgement bias in mice was examined. Mice were trained with two distinct odour cues (vanilla or apple) predicting either a palatable or an unpalatable almond piece. Subsequently their reaction to mixtures of both odours, the ambiguous stimuli, was investigated. Mice of the BALB/cJ and 129P3/J inbred mouse strains (high initial anxiety and low initial anxiety phenotypes respectively) were tested. While BALB/cJ mice showed odour association learning and showed intermediate reactions to the ambiguous cues, 129P3/J mice did not discriminate between the cues. Additionally BALB/cJ mice that were tested under more aversive white light conditions revealed a higher latency to approach the almond piece than mice tested under less aversive red light conditions. The ambiguous stimulus however was interpreted as negative under both test conditions. Brain c-Fos expression levels (a marker for neuronal activity) differed between the BALB/c/J and 129P3/J in the lateral amygdala and the prelimbic cortex, indicating differences in ambiguous information processing between the strains. The behavioural results suggest that the present judgement bias test might be used to assess emotional states in at least BALB/c mice, however further research on both behaviour and on the involved brain mechanisms is necessary to confirm this idea.

220. The effects of stress on cancer progression: A comprehensive literature review of animal models

In humans, affective states can bias responses to ambiguous information: a phenomenon termed judgment bias (JB). Judgment biases have great potential for assessing affective states in animals, in both animal welfare and biomedical research. New animal JB tasks require construct validation, but for laboratory mice (Mus musculus), the most common research vertebrate, a valid JB task has proved elusive. Here (Experiment 1), we demonstrate construct validity for a novel mouse JB test: an olfactory Go/Go task in which subjects dig for high- or low-value food rewards. In C57BL/6 and Balb/c mice faced with ambiguous cues, latencies to dig were sensitive to high/low welfare housing: environmentally-enriched animals responded with relative ‘optimism’ through shorter latencies. Illustrating the versatility of this validated JB task across different fields of research, it further allowed us to test hypotheses about the mood-altering effects of cancer in male and female nude mice (Experiment 2). Males, although not females, treated ambiguous cues as intermediate; and males bearing subcutaneous lung adenocarcinomas also responded more pessimistically to these than did healthy controls. To our knowledge, this is the first evidence of a valid mouse JB task, and the first demonstration of pessimism in tumor-bearing animals. This task still needs to be refined to improve its sensitivity. However, it has great potential for investigating mouse welfare, the links between affective state and disease, depression-like states in animals, and hypotheses regarding the neurobiological mechanisms that underlie affect-mediated biases in judgment.

The effect of repeated testing on judgement biases in sheep

Testing judgement biases of animals may provide insight into their affective states; however important questions about methodologies need to be answered. This experiment investigated the effect of repeated testing using unreinforced, ambiguous cues on the response of sheep to a go/no-go judgement bias test. Fifteen sheep were trained to differentiate between two locations, reinforced respectively with feed (positive) or with the presentation of a dog (negative). The responses to nine ambiguous locations, positioned between the positively and negatively reinforced locations, were tested repeatedly over 3 weeks. Sheep exhibited a symmetrical gradation in response to ambiguous locations between the positive and negative reinforcers. There was a significant decline (P=0.001) in the total number of approaches to the ambiguous positions over time (weeks). This effect of time suggests that sheep learnt that the ambiguous locations were unrewarded. This result supplies evidence of a limitation identified in current judgement bias methodology, due to repeated testing, which has the potential to provide misleading results.

Reduction of fear in Japanese Quail chicks ( Coturnix coturnix japonica) via genetic selection, early environmental enrichment and regular handling

The interaction between cognition and emotions represents previously unforeseen source of information for the animal welfare science. The prototype study of Harding et al. (2004) draw the attention of many researchers to the phenomenon of cognitive bias in animals. Their original approach using operant discrimination training as the basis of the judgement bias test, however, was replaced in many later studies by methods requiring less training, such as the spatial judgement task. The aim of this study was to validate the operant conditioning based cognitive bias test for Japanese quail and investigate the effect of housing conditions (wire cage vs. deep litter pen) on the affective states using this test. Housing conditions were chosen since they may have a wide range of influences on poultry, ranging from behaviour to brain morphology. Quail hens were first trained in an operant discrimination task (contrasting shades of grey) to respond by pecking at the positive cue associated with reward and to refrain from pecking at the negative cue to avoid punishment. The significant differences in the proportion of responses to positive and negative cue were observed very soon (session 1–3) and the quails reached the discrimination criterion (successive discrimination on 3 consecutive days) in 7–9 sessions. In the judgement bias tests the quails were in addition to pretrained cues exposed to three ambiguous cues (shades of grey intermediate between the positive and negative cue). We hypothesised that the quail hens kept in the deep litter pens will be more ‘optimistic’ in ambiguous situations than the quails kept in the wire cages. In two out of four experiments there were no significant effects of housing on the proportion of responses to the ambiguous stimuli. In one experiment deep litter housed birds responded more to the ambiguous stimuli than the caged ones, but after the exchange of environments the same birds housed in cages still responded more to the ambiguous cue. In the last experiment not only the responses to the ambiguous stimuli were lower in deep litter housed quails, but also the responses to the positive cues. Based on these results we have concluded that either the differences between the housings were not large enough, or the length of the housing was not long enough, to induce stable behavioural differences detectable by the operant cognitive bias tests. Using the given judgement bias test design we have failed to validate it as a tool for the assessment of changes in affective states induced by housing conditions in Japanese quail. Nevertheless, further refinement of the test design especially in relation to possible loss of ambiguity problem is necessary.