A snapshot is all it takes to encode object locations into spatial memory

This study examines the encoding of multiple object locations into spatial memory by comparing localization accuracy for stimuli presented at different exposure durations. Participants in the longest duration condition viewed masked displays containing 1-10 discs for 1-10 s (durations typically used in simple span tasks), and then reported the locations of these discs on a blank screen. Compared to conditions that presented the same stimuli briefly for 50 or 200 ms (exposures more typical of simultaneous spatial arrays), localization accuracy did not improve significantly under longer viewing durations. Additionally, a clustering analysis found that responses were spread among different clusters of discs and not focused on individual clusters, regardless of viewing duration. A second experiment tested this performance for displays containing two distinct clusters of discs to determine if clearly grouped subsets of objects would improve performance, but there was no substantial improvement for these two-cluster displays when compared to displays with one cluster. Overall, the results indicate that spatial information for a set of objects is extracted globally and quickly, with little benefit from extended encoding durations that should have favored some deliberative form of grouping. Such results cast doubt on the validity of Corsi blocks or equivalent common neuropsychological tests purportedly designed to evaluate specifically spatial short-term memory spans.