Proceedings of the Annual Meeting of the Cognitive Science Society

In real world contexts of reasoning about evidence, that evi-dence frequently arrives sequentially. Moreover, we often can-not anticipate in advance what kinds of evidence we will even-tually encounter. This raises the question of what we do to ourexisting models when we encounter new variables to consider.The standard normative framework for probabilistic reasoningyields the same ultimate outcome whether multiple pieces ofevidence are acquired in sequence or all at once, and it is in-sensitive to the order in which that evidence is acquired. Thisequivalence, however, holds only if all potential evidence isincorporated in a single model from the outset. Hence little isknown about what happens when evidence sets are expandedincrementally. Here, we examine this contrast formally and re-port the results of the first study, to date, that examines howpeople navigate such expansions.