Cognitive bias as an indicator of animal emotion and welfare: Emerging evidence and underlying mechanisms
Accurate assessment of animal emotion (affect) is an important goal in animal welfare science, and in areas such as neuroscience and psychopharmacology. Direct measures of conscious emotion are not available, so assessment of animal affect has relied on measures of the behavioural and physiological components of affective states. These are important indicators but have some limitations (e.g. measuring emotional arousal rather than valence (positivity vs negativity)). Human psychology research suggests that changes in cognitive function (information processing) can also be reliable indicators of emotional state (especially valence). For example, people in negative states attend to threats, retrieve negative memories, and make negative judgements about ambiguous stimuli more than happier people. Here we review a new research area investigating the possibility that such affect-induced ‘cognitive biases’ also occur in animals. We focus on a novel ‘judgement bias’ paradigm in which animals are trained that one cue predicts a positive event and another cue predicts a less positive/negative event, and are then presented with ambiguous (intermediate) cues. The hypothesis is that animals in a negative affective state will be more likely to respond to (‘judge’) these ambiguous cues as if they predict the negative event (a ‘pessimistic’ response), than animals in a more positive state. Recent studies of rats, dogs, rhesus monkeys, starlings and humans provide face-value support for this hypothesis. We discuss the strengths and weaknesses of the affect manipulation treatments used in these studies, and the possibility that treatment-induced changes in feeding motivation, general activity and learning are responsible for the effects observed, and we consider whether the type of bias observed and the precise design of the judgement bias task can provide information about different types of affective state. Judgement biases may result from the influence of affect on decision-making processes including attention to and perception of the ambiguous cue, evaluation of the value and probability (expected utility) of the outcomes of different responses, and action selection. Affect might also modulate general tendencies of loss, risk and ambiguity aversion, hence biasing decisions. We discuss these possibilities in relation to theory and findings from neurobiological and psychological studies of decision-making, in order to better understand the potential mechanisms underlying judgement biases. We conclude with some specific recommendations for study design and interpretation, and suggestions for future research in this area.