Lateralization of visuospatial processing in the bottlenose dolphin (Tursiops truncatus)

Two adult female bottlenose dolphins were tested for cerebral asymmetries i n the visuospatial domain. The animals learned under binocular conditions a three-choice spatial discrimination task with three hoops positioned along a line in the middle of the tank. During a correct trial the dolphins had to swim from a starting position at the tanks wall through one of the hoops , come back to the starting position, choose another hoop, swim back to sta rt and finally swim through the third hoop. For such a trial to be correct, the animals had to swim through all three hoops in a any sequence without omitting or re-using one of them. After reaching criterion binocularly, mon ocular trials (one eye covered with an adherent suction cup) were introduce d where the dolphins carried out the same task alternatingly under left or right eye seeing conditions. For both animals, the right eye performance wa s clearly superior to that of the left eye. Binocular and right eye perform ances were similar. As a result of the complete decussation at the optic ne rve, this right eye superiority suggests a left-hemispheric dominance for t he processing of visuospatial information. This is a remarkable deviation f rom the usual right hemisphere advantage for these kind of tasks found in d ifferent species of mammals and birds. (C) 2000 Elsevier Science B.V. All r ights reserved.