Figure 6.

Endurance of the traces of learning in the midbrain auditory localization pathway of the barn owl. Juvenile owls adjusted to R23° prisms. The prisms were then removed for a period of at least 6 months. The ability of the ITD map in the optic tectum to shift in response to prisms was tested again after the owls reached adulthood. Barn owls reach adulthood at about 7 months old. (A) Adjustments of tectal ITD tuning (measured as shown in Fig. 2C) in an adult owl that had adjusted to R23° prisms as a juvenile. The plot shows mean and standard deviation of the shift in best ITDs relative to predicted normal, measured at various ages. Shaded regions represent periods of experience with prisms of different strength or direction, as indicated above. Adaptive adjustment to L23° prisms would have been above the 0-μs line. Regardless of the strength or direction of the prisms, adult adjustment is limited to the range of juvenile adjustment. (B) Shift of ITD tuning in three prism-reared (black) versus two normal (gray) adults. The two normal adults had no prior experience with prisms. The three prism-reared adults had adjusted to R23° prisms previously as juveniles (Left). All adult owls were over 1 year old. Data are from Knudsen (37).