Dr. Laurence Harris
York University

Finding your orientation and the perceptual upright in (and off) this crazy mixed up world.

What's up? The orientation in which we expect polarized objects to be ('upright')?  Or the perceived direction of gravity?  We could choose either depending on the situation and the instructions. These directions turn out not necessarily to be aligned although both depend on visual cues, the orientation of your body (where your head is) and gravity. In this talk I will describe how we can measure these directions and how these cues are combined to produce them - it turns out not to be entirely predicable from the reliability of the cues. I will then dissect, using the flexibility of virtual reality, the visual cues we use to identify the roles of the structure (the walls, floor and ceiling - low spatial frequencies - dorsal pathways) and the contents (objects and furniture within the environment - high spatial frequencies - ventral pathways). And by the way, what's the 'floor' anyway? What is the contribution of the room's structural features and the orientations of gravity and the body to the perception of which surface this is? These sorts of questions are particularly germane in ambiguous environments when one or more of the cues are taken away. In space no-one can hear you scream.