Sound Map Plasticity
At Stanford, Knudsen studied the plasticity of the auditory sound map, discovering that associations between the auditory cue values of the map and the locations in space that they represent can be altered by both auditory and visual experience.
Knudsen altered owls’ auditory cues by plugging one ear or removing the ruff feathers and preaural flaps. Initially this caused the birds to inaccurately judge sound source location, since the cues normally associated with each location in space had been changed. However, over time, the map shifted to restore a normal auditory sound map, aligned with the visual space map, despite the abnormal cues. New associations were formed between the abnormal cue values and the spatial locations they now represented, adjusting the map to translate the cues the bird was receiving into an accurate representation of its environment. This adjustment happens most rapidly and extensively in young birds. However, the map never perfectly reflects abnormal experience, even when cues are altered so early that the bird never experiences normal cues. This indicates that there is some innate “programming” of the map to reflect typical sensory experience.
In 1994, Knudsen disproved the idea that the auditory sound map is not long plastic in the adult bird; the plasticity appears to have a critical period. Earlier work had indicated that alteration of the sound map by experience was restricted to a period during development, and once this window of plasticity had passed, subsequent changes would not occur. In work done with Steven Esterly and John Olsen, he showed that adult animals retain plasticity, although to a lesser degree than younger animals. The adult auditory sound map is more readily altered if the bird was exposed to abnormal stimuli earlier in life, during a sensitive period. This shows that the owl’s brain forms functional connections during early abnormal experience which can be reactivated upon the return of abnormal stimuli.
Read more about this topic: Eric Knudsen
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