Aspects of a cognitive neuroscience of mental imagery.

Although objects in visual mental images may seem to appear all of a piece, when the time to form images is measured this introspection is revealed to be incorrect; objects in images are constructed a part at a time. Studies with split-brain patients and normal subjects reveal that two classes of processes are used to form images--ones that activate stored memories of the appearances of parts and ones that arrange parts into the proper configuration. Some of the processes used to arrange parts are more effective in the left cerebral hemisphere and some are more effective in the right cerebral hemisphere; the notion that mental images are the product of right hemisphere activity is an oversimplification.