Hemispheric processing of categorical and coordinate spatial relations in vision and visual imagery

Right-handed subjects participated in a visual half-field experiment using "clock" stimuli. For the Categorical task, subjects indicated whether the long and short hands of a clock were above or below the horizontal midline of the dial. For the Coordinate task, they indicated whether the long and short hands of a clock formed an angle that is more or less than 60 degrees. For both tasks, clock stimuli were either analog clocks (Visual version) or digital clocks from which subjects generated images of analog clocks (Imagery version). The results indicated that for both the Visual and Imagery versions, there was a nonsignificant trend toward a left hemisphere advantage in the Categorical task, whereas there was a significant right hemisphere advantage in the Coordinate task. Implications of the results were discussed from the viewpoints of task factors in hemispheric processing of visual imagery, Kosslyn's (1987, 1994) computational model of vision and visual imagery, and vision/imagery isomorphism.