Pettigrew has made major contributions to our knowledge of the comparative physiology of binocular vision, with more recent extensions to the fields of binaural hearing and somatic sensation. He was the first person to clarify the neurobiological basis of stereopsis when he described neurons in the visual cortex sensitive to binocular disparity and he has continued to influence this field with seminal papers on both the ontogenetic development and evolution of binocular neurons. Of note in the former area of visual development are his recent studies indicating a role for non-visual pathways in the phenomenon of developmental plasticity during the postnatal "critical period". Important in the latter area is his discovery that owls have independently evolved a system of binocular neurons like those found in mammals.