Boundary extension during naturalistic viewing.

Boundary extension refers to a phenomenon in which individuals are likely to remember an image as having more content beyond its actual borders, mistakenly adding details that might have been just beyond the original edges. Despite the wealth of research published about the topic over many decades, most research has used simple two-dimensional (2D) images as stimuli. Consequently, there is insufficient evidence that boundary extension as a phenomenon generalizes to real-world scenarios with naturalistic viewing behavior. To address this gap, we designed a virtual reality (VR) experiment during which the participants (N = 60) were freely able to visually explore naturalistic three-dimensional indoor environments surrounding them. In the experiment, each participant visited each of the 20 virtual rooms twice: first to view the scene and then to complete a task. Their task during the second visit was to move to the location from which they had originally viewed the scene, hence matching their view of the scene to what they remembered seeing before. Especially for close-up views, participants ended their task at a location where their field of view of the scene was wider compared to the initial view, hence indicating boundary extension. The effect was also greater when the movement direction was forward from a wider field of view than that of the original view. Both findings are consistent with previous research and demonstrate that boundary extension is not limited to looking at 2D images but can also occur during naturalistic viewing scenarios. As our method showed no visible boundaries in the stimuli, our results suggest that the existence of such boundaries is not critical for eliciting boundary extension.