Dubois, Magda; (2022) Computational and cognitive mechanisms of exploration heuristics. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Should I leave or stay in academia? Many decisions we make require arbitrating between novelty and the benefits of familiar options. This is called the exploration-exploitation trade-off. Solving this trade-off is not trivial, but approximations (called ‘exploration strategies’) exist. Humans are known to rely on different exploration strategies, varying in performance and computational requirements. More complex strategies perform well, but are computationally expensive (e.g., require to compute expected values). Cheaper strategies, i.e., heuristics, require less cognitive resources but can lead to sub-optimal performance. The simplest heuristic strategy is to ignore prior knowledge, such as expected values, and to choose entirely randomly. In effect, this is like rolling a dice to choose between different choice options. Such ‘value-free random’ exploration strategy may not always lead to optimal performance but allows to spare cognitive resources. In this thesis, I investigate the mechanisms of exploration heuristics in human decision making. I developed a cognitive task allowing to dissociate between different strategies for exploration. In my first study, I demonstrate that humans supplement complex strategies with exploration heuristics and, using a pharmacological manipulation, that value-free random exploration is specifically modulated by the neurotransmitter noradrenaline. Exploration heuristics are of particular interest when access to cognitive resources is limited and prior knowledge uncertain, such as in development and mental health disorders. In a cross-sectional developmental study, I demonstrate that value-free random exploration is used more at a younger age. Additionally, in a large-sample online study, I show that it is specifically associated to impulsivity. Together, this indicates that value-free random exploration is useful in certain contexts (e.g., childhood) but that high levels of it can be detrimental. Overall, this thesis attempts to better understand the process of exploration in humans, and opens the way for understanding the mechanisms of arbitration between complex and simple strategies for decision making.

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