Psychologically informed patient education combined with exercise intervention is associated with improvements in tibial loading regulation, joint kinematics, and kinesiophobia in runners with medial

The popular example of the half-filled glass of water and its interpretation as “half full” or “half empty” illustrates how people differ in the way they judge ambiguous information. Commonly, these different interpretations are referred to as more “optimistic” or more “pessimistic” judgments (terms hereafter used without quotation marks). Scientifically, optimism and pessimism thereby reflect an individual’s general tendency to expect either rewarding or aversive outcomes in ambiguous situations and can be conceptualized as two opposing ends of a spectrum (). For simplicity, however, we will refer to an individual’s position on this spectrum only as its “optimism level” in the following. Adopting this concept from human psychology, optimistic and pessimistic decision-making has been used as a proxy in animal welfare science to assess emotional states of animals (). More specifically, so-called “cognitive judgement bias tests” have been developed to analyze an animal’s response toward ambiguous stimuli. Thereby, animals interpreting ambiguous cues more optimistically are assumed to be in a more positive emotional state than animals interpreting ambiguous cues more pessimistically (). Typically, animal welfare studies make use of such cognitive judgement bias tests to investigate modulations of emotional state, for instance, by changing environmental enrichment [e.g., ()], mimicking play behavior () or inflicting pain (). Hereby, “state” refers to a transient and context-dependent condition, observable only at specific moments in time and influenced by situational factors (). However, more recently, researchers have started to also investigate a potential “trait” dimension of optimism and pessimism. This interest builds on earlier work on individual differences in behavior that are consistent across time and/or contexts, commonly referred to as animal personality in the literature (). Indeed, individuals of the same population have been found to differ consistently in their behavior, with some individuals being shyer, some bolder, some less and some more aggressive than others (, , ). Correspondingly, temporally consistent inter-individual differences in optimism levels have been reported for 3 days in bottlenose dolphins () and wild house mice () and for 25 days in dairy calves (). In laboratory rodents, optimism levels were even found to be consistent across 7 weeks in mice () and for a time span of 10 weeks in rats (). Together, this evidence supports the assumption that cognitive judgement bias can comprise both a trait and a state dimension (, ). “State optimism” thereby captures optimism levels shown at particular moments in time and is potentially modulated by situational factors, while “trait optimism” describes an individual’s general tendency to make more optimistic or more pessimistic judgments, i.e., to behave consistently over time. Clearly distinguishing between state and trait optimism, however, remains difficult since the line between the two dimensions appears to be blurred. For instance, trait optimism may only stabilize with increasing age (), which complicates the distinction between state-dependent fluctuation and not fully established trait optimism. Besides that, trait and state optimism are also likely to interact with each other, since a trait optimist may react differently to a negative or positive experience than a trait pessimist. Rygula and colleagues (), for example, showed that rats characterized as trait pessimists exhibited greater levels of stress-induced anhedonia following restraint stress than trait optimists. At the same time, restraint stress led to a greater negative cognitive bias in all animals, regardless of underlying trait optimism or pessimism. However, hardly any further studies have systematically examined both trait and state optimism as well as possible interactions within a single study.