Verbal labeling, gradual decay, and sudden death in visual short-term memory

Zhang and Luck (Psychological Science, 20, 423-428, 2009) found that perceptual memories are lost over time via sudden death rather than gradual decay. However, they acknowledged that participants may have instead lost memory for the locations of objects. We required observers to recall only a single object. Although the paradigm eliminated the need to maintain object-location bindings, the possibility that observers would use verbal labels increased. To measure the precision of verbal labeling, we included explicit verbal-labeling and label-matching trials. We applied a model that measured the contributions of sudden death, gradual decay, and verbal labeling to recall. Our model-based evidence pointed to sudden death as the primary vehicle by which perceptual memories were lost. Crucially, however, the sudden-death hypothesis was favored only when the verbal-labeling component was included as part of the modeling. The results underscore the importance of taking into account the potential role of verbal-labeling processes in investigations of perceptual memory.