This is a guest post by Aaron Couch, one of Greta’s top student writers for Spring 2007
When looking out a window, or watching a movie in a theater, the image you see is typically presented as right-side-up. Let’s say though, that you’re lying on your side in bed and looking out a window at your backyard. Both your internal gravity sense organs and the orientation of scenery (trees, buildings) tell you that you’re actually seeing a “tilted” image, and your mind immediately tells you which part of the scene is “up”.
In a similar vein, a team led by Ian P. Howard performed research that challenged our mental “visual-righting” system by placing perceived images and our gravity sense organs in conflict. In their research, participants laid down on a bed and looked straight up. Directly above them was a mirror, tilted to display the wall behind them. So, with their own eyes, the person was looking “up” at a ceiling, but the mirror reflected an image presented on the wall.
An image was projected onto the surface the participant was viewing. Two sets of scenes were shown, some with intrinsic polarity (apparent “up” and “down” directions), like an upright chair or human manikin; and a second set to investigate extrinsic polarity, such as a shelf, a ball on a shelf, and a ball “under” a shelf. When presented with the chair or manikin, most people believed they were actually looking directly at a right-side-up scene, or a “wall” in front of them, although their eyes and body were facing upwards. The presented visual scene took precedence over the viewers’ gravity sense organs!
Notice however that an unnatural visual situation, such as the ball directly under a shelf, does not indicate the rules of gravity. Therefore, more viewers saw this “correctly” as an image on the ceiling above them. On the other hand, a ball sitting on a shelf shows a natural situation, implying the presence of gravity and therefore, uprightness.
In a visual-righting illusion your gravitational senses override your visual perception, whereas in a levitation illusion your visual senses override your gravitational perception. According to Howard’s team, some of the most interesting real-life situations of misperceived orientation occur for astronauts in space. Imagine flying back to earth in a shuttle and seeing earth “above” you when you are in reality upside-down. This provides somewhat of a parallel to visual-righting and levitation illusions, except that for astronauts, the absence of both gravity and visual orientation really throws perception into a bind. But then is there really such a thing as “up” or “down” in space?
Howard, I., Hu, G., Saxe, R., & Zacher, J. (2005). Visual orientation in a mirror world tilted 90°. Perception, 34, 7-15.