Relevance and rationalisation in the Wason selection task

Evans' (e.g., 2006) heuristic-analytic theory of the selection task proposes that card selections are triggered by relevance-determining heuristics, with analytic processing serving merely to rationalise heuristically-cued decisions. Evans (1996) provided evidence for the theory by setting up an inspection-time paradigm. He used computerpresented selection tasks and instructions for participants to indicate (with a mousepointer) cards under consideration. The theory predicts that longer inspection times should be associated with selected cards (which are subjected to rationalisation) than with rejected cards. Evans found support for this idea. Roberts (1998b) however, argued that mouse-pointing gives rise to artefactual support for Evans' predictions because of biases associated with the task format and the use of mouse pointing. In the present thesis all sources of artefact were eradicated by combining careful task constructions with eye-movement tracking to measure directly on-line attentional processing. Across a series of experiments good evidence was produced for the robustness of the inspection-time effect, supporting the predictions of the heuristicanalytic account. It was notable, however, that the magnitude of the inspection-time effect was always small. A further experiment separated the presentation of rules from associated cards to avoid possible dilution of the inspection-time effect arising from parallel rule and card presentation. However, the observed inspection time effect remained small. A series of experiments utilising think-aloud methods were then employed to test further the predictions concerning relevance effects and rationalisation processes in the selection task. Predictions in relation to these experiments were that selected cards should be associated with more references to both their facing and their hidden sides than rejected cards, which are not subjected to analytic rationalisation. Support was found for all heuristic-analytic predictions, even .,' . where 'select/don't select' decisions were enforced for all cards. These experiments also clarify the role played by secondary heuristics in cueing the consideration of hidden card values during rationalisation. It is suggested that whilst Oaksford and Chater's (e.g., 2003) information gain theory can provide a compelling account of our protocol findings, Evans' heuristic-analytic theory provides the best account of the full findings of the thesis. The mental models theory (e.g., Johnson-Laird & Byrne, 2002) fares less well as an explanation of the full dataset.