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

Abstract

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.

Dissecting the links between reward and loss, decision-making, and self-reported affect using a computational approach

“…Accordingly, the relationship between decision-making and both the average earning rate and previous outcomes would be consistent with previous findings from animal studies showing that risk and exploration can become greater as overall conditions become less favourable [51,52], a trend that may be explained by individuals in poorer conditions having 'little to lose'. Why this appears to be more evident in a short-time window (within-task) compared to a longertime window when less favourable pre-task conditions are often associated with less risky within-task decision-making [15] requires further investigation.…”

“…This distinction is particularly pertinent in research where decisions on serial trials yielding reward or loss/punishment are used to probe the influence of affective states and disorders on risk-taking and reward sensitivity. The resulting decision-making profiles are proposed as markers of these states (e.g., Iowa Gambling task [5][6][7]; Balloon Analogue Risk Task [8][9][10]; Reward Responsiveness Task [11,12]; Judgement Bias Task [13][14][15]). In most studies, decision-making data across test sessions are summarised into single statistics such as the number of cards selected from more favourable decks, the average number of 'balloon' pumps, the overall response bias as a marker of reward responsiveness, or the proportion of 'optimistic' responses.…”

“…The judgement bias task was originally designed [13], and has since been widely used [14,15], as a translational paradigm in which decision-making under ambiguity could be used as an indicator of an individual's affective state. In the task, participants are trained to discriminate between two stimuli and make different responses to each (typically 'go' or 'stay'/'no-go') in order to either obtain a reward or avoid a punisher.…”

“…Decision-making in the judgement bias task, particularly trials with perceptually ambiguous stimuli, is considered to be indicative of a longer timescale notion of affective state, or 'mood'. Specifically, more 'optimistic' decision-making, as indicated by an excess proportion of 'optimistic' as opposed to 'pessimistic' decisions made across a test session, is typically associated with more positively valenced affect [14,15,24]. This decision-making profile is hypothesised to reflect approximate sufficient statistics about the characteristics of the individual's interaction with and experience of the rewarding and punishing features of their environment [22,25,26].…”

Using judgment bias test in pet and shelter dogs (Canis familiaris): Methodological and statistical caveats

“…It is now widely agreed that a positive affective state (comprising both the longer term background mood state and shorter-term discrete emotions [ 1 ]), and not only physical health, is a crucial component of animal well-being [ 1 ]. Animal welfare science and biomedical research have attempted to establish scientific and reliable measures of affective states in non-human animals, with the cognitive bias approach being one of the most commonly applied tests across species (for reviews see [ 2 – 5 ]; for critical analyses see [ 6 , 7 ]; for a meta-analysis on how pharmacological manipulations influence judgment bias see [ 8 ]). Cognitive bias theories concern the influence of emotional states on cognitive functions (such as attention, memory and judgment) [ 3 , 7 ].…”