Elementary, my dear Wason: the role of problem representation in the THOG task.

The present study was concerned with Wason's THOG problem, a hypothetico-deductive reasoning task for which performance over the past 20 years has typically been very poor (< 20% correct). We examined the hypothesis that incorporating a quasi-visual context into the problem statement would make both the binary, symmetric tree structure and solution principle of the THOG task clearer and thus facilitate performance. A version of O'Brien et al.'s (Q J Exp Psychol 42A:329-351) Blackboard THOG problem, that specifies each branch of the tree by describing a specific location for each possible color-shape combination, was used to test this hypothesis. Substantial facilitation was both observed (68% correct) and replicated (73% correct), and it was also shown that it is necessary to provide a representation of both sides of the tree to obtain this level of facilitation. The implications of these results for human deductive reasoning are considered.