Characteristics of positron emission tomography (PET) images that limit human ability to accurately perceive the information the images contain are discussed. They are relatively low spatial resolution, a lack of apparent anatomical information and the expression of metabolic activity in terms of brightness levels (gray levels), which are not efficiently determined by the human visual system. These affect how clearly the 3-D structures contained in the reconstructed 3-D images can be seen. The use of pseudocolor to visualize different levels of activity expressed by brightness and shading to accentuate depth and shape information is described. To further enhance the brightness contrast of a surface with its neighboring areas, stereo and motion were used as depth cues. >