Visual form discrimination from color or motion cues: functional anatomy by positron emission tomography.

To explore the extent to which various cortical functional pathways are involved in processing and analyzing different types of information that yield the same perceptual entity, we mapped anatomical structures in the human brain participating in the discrimination of visual forms mediated either by motion or color cues. Changes in regional cerebral blood flow were measured in 10 young male volunteers with positron emission tomography and with [15O]butanol. During the measurements, the subjects performed four visual discrimination tasks (form-from-motion, motion alone, form-from-color, and color alone discrimination). The individual regional cerebral blood flow images were standardized in shape and size with the help of a computerized brain atlas. Subtraction images were determined and averaged across data from all subjects. The resulting images were analyzed for statistically significant changes between specific and reference tasks. The discrimination of form by means of motion cues activated functional fields bilaterally in the inferior and lateral occipital gyri, in the lingual, anterior cingulate, middle frontal and orbitofrontal gyri, and in the left fusiform and right inferior temporal gyri. Form discrimination by color cues resulted in activation bilaterally in the inferior temporal, lateral occipital, and orbitofrontal gyri, the left precuneus and intraparietal sulcus, and the right precentral gyrus. The regions engaged in the two kinds of form discrimination did not overlap, demonstrating that differences in visual forms mediated by color or motion cues are processed and analyzed by disparate networks of functional fields in human cerebral cortex.