The cerebral laterality of mental image generation in normal subjects.

This research was an attempt to replicate and extend a published study that reported a left hemispheric locus for the generation of mental images. Several methodological problems were addressed, the stability of effects was assessed by repeating the experiment, and P300 latency was measured. A lateralized visual choice reaction time task was performed twice, once without the use of imagery and once with imagery. In each visual field, the use of imagery produced a speeding of reaction times when the target stimuli matched the image generated by the subject. A similar effect was present for P300 latency, and was still present in the reaction time data after partialling out the P300 latency effect. These results indicate that mental imagery can speed both stimulus evaluation and response processing. There was no difference in the amount of speeding for images in the two hemifields, providing no evidence for a preferential locus of mental image generation in either cerebral hemisphere.