The temporal instability of cognitive performance

This thesis contributed to the empirical knowledge of cognitive variability through psychometric modeling of theory-based descriptive and mechanistic structures fitted to neural and behavioral data. We learned that cognitive variability is multidimensional: varying across tasks (Chapter 4) and timescales (Chapter 5). Chapter 3 taught us that, in a battery of response time tasks, cognitive variability is a correlate of inattention problems and is modulated by attentiveness as predicted by a noradrenergic mechanism. The results of Chapter 6 showed us that cognitive variability in a simple response-time task can be manipulated using methylphenidate, a transporter blocker of dopamine and noradrenaline. But contrary to prior hypotheses, the effect of methylphenidate could not be attributed to dopamine or a change in neural variability. Lastly, by examining the neural antecedents of cognitive variability, we learned that cognitive variability in a working memory task is driven by uncertainty in our encoded representations, which in turn depends on the neural resources spent to encode stimuli in the preceding trial (Chapter 7).