Visual Short-Term Memory: is Capacity Dependent on Stimulus Complexity?

Several recent studies have explored the nature and limits of visual short-term memory (VSTM) (e.g. Luck & Vogel, 1997). A VSTM capacity limit of about 3 to 4 letters has been found, thus confirming results from earlier studies (e.g. Sperling, 1960). However, Alvarez and Cavanagh (2004) have argued that VSTM capacity is dependent on visual complexity rather than the number of objects. We hypothesise that VSTM capacity is dependent on both the objective and the subjective complexity of visual stimuli. Contrary to Alvarez and Cavanagh, who argue for objective complexity, it seems that subjective complexity - which is dependent on the familiarity of a given stimulus - plays a more important role than the objective visual complexity of the objects stored. In several studies, we explored how familiarity influences the capacity of VSTM and our results indicate that VSTM capacity for familiar items is larger irrespective of visual complexity.