Relational information in visual short term memory and context induced change perception

Abstract

Most studies about the capacity of VSTM implicitly consider each stored unit is stored independently of the others. Nevertheless there is evidence that relational information exists within each feature dimension in VSTM (Jiang et al., 2000), links information from individual units and needs no attention for its establishment (Vidal et al., 2005). The present study examines the role of relational information. In a change detection paradigm we presented a sample screen composed of 4 colored squares and, after a blank, a test screen where one of the items was cued as target. Subjects had to detect a target color change (Exp1,3–5), to rate their level of certitude (Exp3) and/or to recall the initial color (Exp1&2). On the test screen the non-target items can disappear (Exp5), change color (Exp1–4)) and be supplemented by four new squares (Exp4). We observed that non-target color changes do not impair change identification but do impair non-change detection performance (Exp1&2) and that subjects are sure to see the target changing even though it did not (Exp3). The same effect was observed when the non-target items disappeared (Exp 5) but not when irrelevant items were added on the test screen (Exp4). We concluded that a changing context induces an illusion of change for the non changing item and that this effect results from memory and not simply perceptual mechanisms. We propose a model of change detection including relational information that explains this “change illusion” and predicts change detection among items not stored in VSTM.