Encoding strategy accounts for individual differences in change detection measures of VSTM

Visual short-term memory (VSTM) capacity is often assessed using change detection tasks, and individual differences in performance have been shown to predict cognitive aptitudes across a range of domains in children and adults. We recently showed that intelligence correlates with an attentional component necessary for change detection rather than with memory capacity per se (Cusack, Lehmann, Veldsman, & Mitchell, 2009). It remained unclear, however, whether different attentional strategies during change detection have most impact during the encoding or maintenance of information. Here we present recent findings from our laboratory supporting the hypothesis that attentional selection during encoding dominates individual differences in change detection measures of visual short-term memory. In a first study, we unpredictably varied whether short-term memory was probed using change detection or whole report, encouraging participants to adopt the same encoding strategy throughout the tasks. Change detection performance of lower-IQ individuals improved. In a second study, we found that deficits in top-down attentional selectivity can be alleviated in participants with low change detection performance by providing helpful grouping information during encoding. Finally, a meta-analysis of neuroimaging data from 112 participants performing a variety of VSTM tasks showed that performance correlates with activity in several parietal and frontal regions during the encoding but not the maintenance phase. Taken together, these results support the notion that encoding strategy and not short-term memory capacity itself largely determines individual differences in visual change detection performance.