Feeney, A. & Leckey, M.
Queen's University, Belfast, UK
Category-based inductive reasoning involves the generalisation of properties from a sample consisting of members of one or more premise categories to members of a conclusion category. People are known to be sensitive to the diversity and size of the set of premise categories so that more diverse and larger samples result in stronger ratings of argument strength. Associative accounts of category-based induction explain both of these sensitivities in terms of a single parallel process that is fast and independent of working memory. Other accounts suggest that there may be multiple resource demanding processes in play. Feeney (2007) showed that sensitivity to both diversity and sample size is correlated with IQ, a finding that is problematic for associative accounts. Here we describe a study that directly investigated the role of working memory in sensitivity to diversity and sample size by placing some participants under cognitive load whilst they reasoned about pictorial premises. Because what people can remember about the contents of reasoning problems may have much to tell us about how they reason (see Sloutsky & Fisher, 2004) we employed an Induction-then-Recognition (ITR) paradigm where participants completed an unexpected recognition memory test after the reasoning task. Sensitivity to sample diversity but not to sample size was significantly affected by a secondary load. Sensitivity to sample size only was associated with faster reasoning times and with poorer recognition memory. These results suggest that sensitivity to sample size involves the application of a simple rule, whereas sensitivity to diversity requires more complicated similarity calculation. Thus, different inductive reasoning phenomena may require different explanations. We will discuss the implications of our results for dual process theories reasoning which predict, contrary to our findings, that correlations with IQ will often be accompanied by effects of a secondary load.