We remember the past as more rewarding than it was: effects of temptation on cheating and visual working memory

Here we report that participants’ visual working memory of an ambiguous cue is biased towards stimuli that are associated with a high reward. Participants saw eight digits presented in a circular arrangement. On some trials, they were asked to report the digit (“Target Digit”) indicated by a jittery cue that was slightly biased in the direction of another digit (“Second Cued Digit”), which was either higher, or lower than the Target Digit. Participants were paid based on the reported digit (higher digits meant higher pay) and not based on the accuracy of their report. In this setting, they could make self-serving mistakes by dishonestly reporting the Second Cued Digit when it was higher than the Target Digit. Replicating prior work, we found that participants frequently made such self-serving mistakes. On other trials, after the digits disappeared, participants were asked to reproduce the direction of the jittery cue, without receiving any pay. This allowed us to test whether participants’ memory of the cue was biased toward high-rewarding digits, and our results showed that it was. We cautiously suggest that self-serving mistakes might result from automatic biases in working memory, which provides an important constraint for theories in behavioral ethics

Temperament, Plasticity, and Emotions in Defensive Behaviour of Paca (Mammalia, Hystricognatha)

Within a species, some individuals are better able to cope with threatening environments than others. Paca (Cuniculus paca) appear resilient to over-hunting by humans, which may be related to the behavioural plasticity shown by this species. To investigate this, we submitted captive pacas to temperament tests designed to assess individual responses to short challenges and judgement bias tests (JBT) to evaluate individuals’ affective states. Results indicated across-time and context stability in closely correlated “agitated”, “fearful” and “tense” responses; this temperament dimension was labelled “restless”. Individual “restless” scores predicted responses to novelty, although not to simulated chasing and capture by humans in a separate modified defence test battery (MDTB). Restless animals were more likely to show a greater proportion of positive responses to an ambiguous cue during JBT after the MDTB. Plasticity in defensive behaviour was inferred from changes in behavioural responses and apparently rapid adaptation to challenge in the different phases of the MDTB. The results indicate that both temperament and behavioural plasticity may play a role in influencing paca responses to risky situations. Therefore, our study highlights the importance of understanding the role of individual temperament traits and behavioural plasticity in order to better interpret the animals’ conservation status and vulnerabilities.

The erroneous signals of detection theory

Signal detection theory has influenced the behavioural sciences for over 50 years. The theory provides a simple equation that indicates numerous ‘intuitive’ results; e.g. prey should be more prone to take evasive action (in response to an ambiguous cue) if predators are more common. Here, we use analytical and computational models to show that, in numerous biological scenarios, the standard results of signal detection theory do not apply; more predators can result in prey being less responsive to such cues. The standard results need not apply when the probability of danger pertains not just to the present, but also to future decisions. We identify how responses to risk should depend on background mortality and autocorrelation, and that predictions in relation to animal welfare can also be reversed from the standard theory.