Averaging model applied to the size-weight illusion

A theoretical model was given for the size-weight illusion based on a principle of information integration. Judged heaviness of lifted weights was assumed to be an average of two pieces of information, weight and size, with the latter receiving negative weighting in the model formulation. Two experiments based on a Weight by Size design gave fair support to the parallelism prediction of the integration model. The hypothesis that Ss were really judging density was shown to imply a divergence prediction, contrary to the data. The theoretical analysis was generalized to include negative, positive, and comparative illusions; these were differentiated according to whether the contextual information was integrated with negative weighting, positive weighting, or served as a yardstick of judgment.