Abstract
Vision plays an important role in our ability to orient. A major factor in self orientation is the perceived direction of up. Previous studies involving perceptual upright (PU: the orientation at which objects are best recognized) have demonstrated a consistent leftward bias in a character recognition task. We hypothesized that this leftward bias may be due to unequal visual orientation cue ratings across the visual field. We assessed the perceptual upright using OCHART (Oriented CHAracter Recognition Task) which measures the orientation at which a letter probe is “perceptually upright” (Dyde et al., 2006 Exp Brain Res. 173: 612). The probe was presented in the centre of a background masked down to a circle subtending 35° and divided into two with a vertical black line separating the two halves. Images on each half were photographs of an outdoor scene upright, tilted clockwise or counter-clockwise by 112.5°, or a grey field of equal average luminance. The effects of the two sides were additive in determining the PU with no obvious dominance of one side or the other. However, when the oriented scene was presented only on one side (with the other side grey) the strongest effect on the probe was found when visual cues were tilted in the same direction as the visual field on which they were presented. Our data suggest that orientation cues presented on the left and right sides of space are weighted approximately equally by the brain. The brain integrates the conflicting visual cues on either side of the visual field when determining perceptual upright.
Canadian Space Agency, Natural Sciences and Engineering Research Council of Canada.