Boundary extension: fundamental aspect of pictorial representation or encoding artifact?

Viewers remember seeing more of a scene than was actually depicted in a photograph, a phenomenon called boundary extension (H. Intraub & M. Richardson, 1989). We tested whether prior warning would eliminate this distortion, by having 81 Ss view 12 photographs of simple scenes for 15 s each after receiving 1 of 3 encoding instructions. All subjects were told to remember each picture in detail. Control Ss received no additional information. Test-informed Ss received prior warning about the type of tests. Demo Ss experienced a demonstration of the phenomenon and were instructed to guard against it. After presentation, a drawing task and a boundary recognition test were administered. Prior warning sometimes reduced, but never eliminated, boundary extension. We suggest the phenomenon reflects activation of scene expectations during perception.