Forgetting and the mirror effect in recognition memory: concentering of underlying distributions.

The mirror effect is a strong regularity in recognition memory: If there are two conditions, A and B, with A giving higher recognition accuracy, then old items in A are recognized as old better than old items in B, and also new items in A are recognized as new better than new items in B. The mirror effect is explained by attention/likelihood theory, which also makes several new, counterintuitive predictions. One is that any variable, such as forgetting, that affects recognition changes the responses to new as well as old stimuli. In terms of underlying distributions, forgetting produces concentering, the bilateral movement of distributions, both new (noise) and old (signal), toward a midpoint. Data from two forced-choice experiments are reported that support the prediction of concentering and other predictions drawn from the theory. It is argued that current theories of memory, which are strength theories, cannot handle these regularities.