No imagination effect on boundary extension

Boundary extension (BE) occurs when people falsely remember perceiving beyond the edges of a presented scene. Theorists argue that BE occurs because people mistakenly attribute information they have generated to the study stimulus-that is, they make a source memory error. Inspired by this idea, in six experiments we tested whether scene details resulting from explicit imagination would be misremembered as actual visual perceptions, resulting in increased BE as compared with standard instructions. In four experiments, undergraduates completed a BE task with separate study and test blocks; in two further experiments, undergraduates completed a trial-by-trial BE task (N = 290). Half of the participants elaborated on the study pictures (imagined smells and sounds, or what was to the left and right of the scene, or what a photographer would see by zooming in or out). Robust BE was found in all experiments, but none of the elaborations modified the size of BE; therefore, BE is not to be affected by explicit elaboration and may be related to spatial rather than visual imagery ability.