Limited capacity for memory tasks with multiple features within a single object.

Memory for multiple features might be limited by the number of features, the number of objects, or both. To focus on the role of features, we tested memory for a variable number of features within a single object. Subjects studied a single ellipse that varied in four features: size, orientation, contrast, and position. We conducted two experiments that differed in how memory was tested. If performance is limited only by the number of objects to be remembered, there should be no effect of the number of relevant features within a single object. Instead, for both experiments, the proportion correct was lower when four features had to be remembered rather than one. The magnitude of these effects varied with the details of the two experiments. Although similar results have been reported for experiments using multiple objects, the present experiments are some of the first to have demonstrated such an effect for a single object. This result is inconsistent with theories in which visual memory has a discrete limit on the number of stored objects, and no limit on the stored features within an object. Instead, it seems likely that objects and features both play roles in limiting performance in memory tasks.