UC Davis

Accurate measures of affective processing in animals are essential to advancing fields ranging from animal welfare science to neuroscience and psychology. However, objective measures of affect are currently unavailable, leading scientists to rely on measurable changes in decision-making (judgement biases) as a proxy for affective processing in various species. Yet, minimal research has been conducted on the connection between decision-making and affect in rhesus macaques, with a lack of focus on validating the judgement bias task as a measure of both affective traits and states. Here, research was conducted to validate whether the judgement bias task captures both stable individual differences in baseline biases, indicative of trait affect, and momentary negative shifts in biases following a negative threat induction, suggestive of shifts in affective states. Additionally, research aimed to determine whether judgement biases were related to affective reactivity, a conventional measure of affective processing obtained from the Human Intruder Test. Results showed temporal stability in individual differences in baseline judgement biases, suggesting the judgement bias task provides a suitable index of trait affect within individuals. Consistently negative baseline judgement biases also predicted a higher overall susceptibility to affective reactivity during the Human Intruder Test. A reduction in response post threat induction compared to baseline measures was also found, reflecting the capturing of categorically negative affective states within individuals. During post threat induction judgment bias testing, shifts in reward valuation were also related to a higher human-directed reactivity during the prior Human Intruder Test. A lack of context stability in individual differences in judgment biases and no relationship between overall affective reactivity and judgement biases demonstrated that baseline trait judgement biases alone could not predict how influential threat induction would be on an individual’s affective processing and thus decision-making. Results validated the judgement bias task as a proxy measure of affective traits and states in captive rhesus macaques. However, additional recommendations must be considered to further our understanding of the link between affect and cognition in non-human primates.