Abstract
In this study, we sought to determine whether representations in visual working memory are stored independently of each other. Just as similarity impairs performance of LTM, similarity should impair working memory performance if representations are not stored independently. To test this hypothesis, we manipulated the similarity of the to-be-remembered items in a change-detection task. On each trial, subjects viewed a sample array consisting of 3 or 4 colored squares, followed by a retention interval and then a test array. The test array was either identical to the sample array or differed in the color of one item, and subjects indicated whether a change was present. The colors of the items were selected from three sets of colors: reddish colors, greenish colors, and bluish colors. On some trials, all the colors in the sample and test arrays were drawn from a single set and were therefore highly similar to each other. On other trials, the colors were drawn from all three sets and were therefore highly dissimilar to each other. In Experiment 1, we found that change-detection accuracy was no better for the dissimilar colors than for the similar colors. However, when we conducted a visual search paradigm using the same stimuli, the reaction time was much slower among similar colors, indicating that our similarity manipulation was robust. In Experiment 2, the stimuli were presented sequentially to avoid any relational encoding of the colors, which could potentially lead to better performance for similar colors. In Experiment 3, multi-feature objects (i.e., color, shape, and orientation) were used that contained identical features on either two dimensions or no dimensions. In all experiments, change-detection accuracy among similar objects was no worse than among dissimilar objects, suggesting that similar representations can be concurrently formed and maintained in visual working memory just as accurately as dissimilar representations.
This research was made possible by grants R01 MH63001 and R01 MH65034 from the National Institute of Mental Health.