Journal of Neuroscience, Vol 9, 3297-3305, Copyright © 1989 by Society for Neuroscience
Visuomotor adaptation to displacing prisms by adult and baby barn owls
EI Knudsen and PF Knudsen
Department of Neurobiology, Stanford University School of Medicine, California 94305.
The capacity of barn owls to adapt visuomotor behavior in response to
prism-induced displacement of the visual field was tested in babies and
adults. Matched, binocular Fresnel prisms, which displaced the visual field
11 degrees, 23 degrees, or 34 degrees to the right, were placed on owls for
periods of up to 99 d. Seven baby owls wore the prisms from the day the
eyelids first opened; 2 owls wore them as adults. Prism adaptation was
measured by the accuracy with which a target was approached and struck with
the talons, a behavior similar to pointing behavior used commonly to assess
prism adaptation in primates. Baby and adult owls exhibited a limited
capacity to adapt this visuomotor behavior. Acquisition of adapted behavior
was slow, taking place over a period of weeks, and was never complete even
for owls that were raised viewing the world through relatively weak (11
degrees) displacing prisms. When the prisms were removed from adapted owls,
they struck to the opposite side of the target. The recovery of strike
accuracy following prism removal was rapid; 7 of 9 owls recovered normal
accuracy within 30 min of prism removal, despite having worn the prisms for
months. This limited capacity for adaptation contrasts dramatically with
the extensive and rapid adaptation exhibited by adult primates exposed to
comparable prismatic displacements. The mechanism of adaptation used by the
owls was to alter the movements employed for approaching targets. Instead
of moving straight ahead, the head and body moved diagonally relative to
the orientation of the head. Thus, in contrast to prism adaptation by
humans that can involve reinterpretation of eye, head, and limb position,
prism adaptation by owls is based on changes in the motor commands that
underlie approach behavior.