Spatial and categorical structure in short-term visual memory

Across different timescales, visual memory differs not only in its functional characteristics – namely its capacity and its duration – but also in its structure. Long-term visual memory is perhaps entirely categorical, while at the shortest latencies visual iconic memory shows signs of pictorial or imagistic structure. In this study we aimed to distinguish these two forms of memory structure, demonstrating differences in long and short term memory using similar stimuli. We confirm earlier results showing that long-term memory relies on the categorical content evoked by seeing scenes, using a standard study-and-test paradigm. With the same paradigm we show that short-term memory seems unaffected by the subtraction of high-level categorical content, implicating pre-categorical structure in memory. With the same stimuli we carry out a discrimination task, with the results suggesting that this pre-categorical structure may be explicitly spatial, the stuff of iconic memory and online vision.