The effect of tilt on the perceptual upright

The perceptual upright (PU), the orientation in which an object is most easily and naturally recognized, is determined by combining visual, gravity, and body cues. Recognizing a character the identity of which depends on its orientation can be used to assess PU. For example, the letter 'p' when rotated 180° becomes the letter 'd'. The transitions from p to d and d to p, when averaged, define PU. This is the orientated character recognition task (OCHART). The PU can be predicted from the weighted vector sum of the orientation of the visual background, gravity, and body. Observers completed OCHART in several body tilts in roll. The PU measured at some body tilts (eg 45°) was not accurately predicted by this simple model. One possible explanation for this is that the nervous system's assessment of the relative weights and directions of vision, gravity, and the body required to determine the PU may depend on the internal representation of the body tilt and the orientation of the eyes in the head