Visuomotor adaptation to displacing prisms by adult and baby barn owls

Abstract

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.

Vision calibrates sound localization in developing barn owls

“…Human observers could detect little difference between the 34" prisms and the 23" prisms when viewing a uniformly textured screen that obscured the magnitude of the displacements. Moreover, the birds that wore these prisms developed normal eye alignment, which requires fused binocular form vision (Knudsen, 1989), and they were able to see small targets at a distance and to use vision to guide their approach and strike (Knudsen and Knudsen, 1989a). Second, the extent of the visual field afforded by 34" prisms was only slightly less than that afforded by the 23" prisms ( Fig.…”

“…Owls raised from the day of eyelid opening viewing the world through displacing prisms continue to commit systematic errors when attempting to lly toward or strike at visual targets (Knudsen and Knudsen, 1989a). Thus, the dominance of vision over sound localization does not depend on the demonstrated validity of visual localization; apparently, visual dominance is innate.…”

“…Sound localization was quantified by measuring the orientation of the head relative to acoustic targets. The companion study (Knudsen and Knudsen, 1989a) demonstrated that the orientation of the head is a reliable indicator of the owl's perception of stimulus source location.…”

“…The owls wore the prisms continuously for months. When tested as juveniles, they had altered sound localization (within limits) to match visual localization, even though visual localization was incorrect (Knudsen and Knudsen, 1989a).…”

Hunting Increases Adaptive Auditory Map Plasticity in Adult Barn Owls

“…Immediately after prisms are mounted, an owl will strike an auditory target accurately because the prisms do not alter auditory space cues. However, like many other species, owls quickly recalibrate their movements based on vision (Knudsen and Knudsen, 1989a). Because movements now are calibrated to the prismatically displaced visual field, the owls must also recalibrate their ITD maps to match the visual maps to reestablish an aligned sensorimotor coordinate frame.…”