In boundary extension (BE), people confidently remember seeing a surrounding region of a scene that was not visible in the studied view. However, the content near image boundaries might be uninteresting, serving only as a background for a central figure.In our experiments, we presented participants with 24 photographs with a defect (cut-out hole or black ink blot). Participants were instructed to memorize the photograph and then either reproduce the size of the hole/blot (BE task) or identify a change (distractor task). In Exp. 1, we showed participants printed photographs (18×13 cm) with cut-out holes. Participants systematically drew smaller holes (87.5% diameter, N=32). When we replaced the holes with black ink blots (Exp. 2), the bias was still present (91.4%, N=30). The computer-based version with size-adjustment of black blots (Exp. 3) yielded similar effects (92.8%, N=30), which disappeared (Exp. 4, 100.7%, N=30) if the probe blot sizes were randomized.We argue that BE occurs in the internal parts of photographs. We explored the effect in different media (paper/screen) and using different response tasks (free recall/adjustment). People show uncertainty in the adjustment tasks and reproduce remembered holes/blots as smaller (consistent with BE) if they are presented with the occluded content in the response phase.
Group size adjustment to ecological demand in a cooperative breeder
