Is there a right way up for vertical symmetry?
Hulleman J., Humphreys GW.
Responses to vertical symmetry are quicker than responses to either horizontal or diagonal symmetric stimuli. However, within vertically symmetric stimuli, we demonstrate a preference for search for stimuli that are upright - where upright stimuli are defined by having a broad base. When participants have to search for vertical symmetry in multiple item displays, their responses are about 50 ms quicker when the items are upright, than when the items are upside down. There was no effect of uprightness in single item displays. The data suggest that 'uprightness' can serve as a guiding factor for visual attention, consistent with prior results indicating ecological constraints on search and visual selection.