Exploring the role of space-defining objects in constructing and maintaining imagined scenes.

It has recently been observed that certain objects, when viewed or imagined in isolation, evoke a strong sense of three-dimensional local space surrounding them (space-defining (SD) objects), while others do not (space-ambiguous (SA) objects), and this is associated with engagement of the parahippocampal cortex (PHC). But activation of the PHC is classically associated with scene stimuli. The comparable neural response within PHC to both full scenes and single SD objects, led us to hypothesise that SD objects might play a more critical role in the construction and maintenance of scene representations than SA objects. To test this we used scene construction and deconstruction paradigms, where participants gradually built and maintained scenes using SD, SA and background (wall, floors) items. By examining the order in which each item was added (and later removed) to (and from) a scene, we could estimate the significance of each item type. In two different experiments, participants chose SD over SA objects and background items as the first and most critical item in their constructed scenes and, more generally, selected SD objects earlier than SA objects across the scene construction process. When deconstructing scenes, participants retained significantly more SD objects than SA objects, and the last remaining object across all scenes was highly likely to be an SD object. SD objects therefore enjoy a privileged role in scene construction and maintenance, and appear to be an essential building block of scenes.