The role of arousal in boundary judgement errors.

Eyewitnesses to a crime rely heavily on their visual memory; however, there are many ways that the details of visual scenes can be missed, or distorted. In particular, for emotional scenes, the "boundaries" are narrowed at retrieval, whereas central details-such as a weapon-are remembered in greater detail. This phenomenon is known as boundary restriction, the reverse of boundary extension whereby people tend to expand the boundaries of a neutral scene at retrieval. In the present series of experiments, we investigated whether arousal is the element of an emotional scene that leads to increased boundary restriction or reduced boundary extension. We presented neutral images to participants either with or without a stress-inducing noise. In Experiment 1a and 1b, at test, participants viewed the image they originally viewed next to the same image but with narrower or wider boundaries and selected which of the two images they originally viewed. In Experiment 2, at test, participants viewed the identical image they originally viewed, but were told the boundaries had been changed. Participants selected the extent to which the images at test had restricted or extended boundaries compared to their memory of the original image. When the noise stressor was present, participants made more boundary restriction errors-selecting the image with narrower boundaries than the original-and fewer boundary extension errors than when the noise was absent. Our data suggest that arousal plays a key role in boundary judgements.