Upper and lower visual field differences in perceptual asymmetries.

A leftward spatial bias has been observed with visuospatial attention tasks, including line bisection and the greyscales task. Upper and lower visual field differences have been observed on various tasks, with a lower visual field advantage occurring for motion, global processing and coordinate spatial judgments. Upper visual field advantages occur for visual search, local processing and categorical judgments. In perceptual asymmetries research, upper and lower visual field differences have not typically been scored separately, as most presentations have been central. Mixed results have made it difficult to determine whether lateral biases are stronger in the upper or the lower visual field. As length of presentation time differed in prior studies, this factor was examined to determine whether it would lead differential biases to emerge in each visual field. The greyscales task was used to investigate the interaction of visual field and presentation time within subjects (N=43). Eye tracking was used during the task and supported the hypothesis of a stronger left bias in the lower visual field. Presentation time and visual field interacted to influence performance. Prolonged presentation led to a stronger leftward bias in the lower visual field whereas the leftward bias was stronger in the upper visual field during brief presentation. Results showed a relation between the lower and left visual fields and the upper and right visual fields, which has not previously been shown in perceptual asymmetries. Further, it is suggested that functional differences between the visual streams could underlie the visual field differences in perceptual asymmetries.