Spatial processing of images and hemisphere function.

Forty subjects performed both of the following tasks. In the imagery task, simple dot patterns were presented for five seconds in free vision, followed by a three second fixation field. Subsequently, a circle was briefly presented in either the right or the left visual field and subjects were required to indicate whether or not the circle surrounded a point previously occupied by a dot. The perceptual task was similar except that the dot patterns remained on the screen while the circle was presented. Reaction times and error data indicated a left visual field advantage on the imagery task only, suggesting a right hemisphere superiority for extraction of spatial information from images.