Hunting and Hearing in Owls

Question 1

Prey localization

Answer 1

locates in azimuth and elevation
owl turns head towards noise with less than 2% error in either place
rotate head up to 270 degrees
location in azimuth depends on time difference between 2 ears
location in elevation depends on intensity difference between 2 ears

Question 2

Space specific neurons

Answer 2

in external nucleus of the inferior colliculus (ICX) of mid brain
each excited by sounds from a particular direction
receptive fields change in orderly way so, ICX acts as map
many listen to space 15 degrees either side of beak, 40 degrees above and 80 degrees below- a fovea
small lesions in ICX cause predictable errors in owls ability to localize
integration

Question 3

Ear structure

Answer 3

single bone connects tympanum to oval window of coclea
cochlea nearly straight
can’t hear as many sounds
separate evolutionary origin to mammals

Question 4

Auditory Neurons

Answer 4

in cochlea hair cells excite sensory neurons
these sensory neurons have axons that carry spikes to brain
sensory neurons from left project to cochlear nucleus on own side
each cochlear nucleus divided into 2
angular nucleus- axons from one branch of sensory neurons and encode time
magnocellular nucleus- axons from another branch and encode intensity

Question 5

Binaural processing

Answer 5

in nuclei on each side of the brain, info from both left and right cochlear nuclei is combined
time difference between L&R converge in laminar nucleus (on each side)
Intensity differences between L& R converge in posterior lemniscus

Question 6

How does the brain measure LR time differences (azimuth)?

Answer 6

in laminar nucleus axons and branches from one ear run parallel to axons and branches from other but from different directions
magnocellular neurons excite laminar nucleus
laminar nucleus acts as coincidence detector- spike if both axons excite it spike simultaneously
marks LR time delay based on its location in array

Question 7

How does the brain measure LR intensity differences (elevation)?

Answer 7

left ear more sensitive to sounds from below and right to sounds from above
LR intensity difference pathway provides info about elevation of sound source
each posterior lemniscus neuron is sensitive to one combination of LR ear intensity difference
Involves both excitation and inhibition
connect with each other as well and angular nuclei
orderly way- map

Question 8

Optic tectum

Answer 8

receives info from ICX
acts as map of space- combines info from different sensory modalities
send axons to brain stem which controls movement of neck

Question 9

Alignment of maps

Answer 9

visual map present at hatching

map of auditory space in ICX develops and is adjusted by reference to map of visual space in optic tectum

Question 10

Eric Knudsen and juvenile owls

Answer 10

1 ear plugged- misdirect gaze but adjustment restores accuracy (auditory map plastic)
Line of sight deflected by 23 degrees with prisms- misdirect gaze but can still direct accurately to source of sound (visual map fixed)
when removed visual but not auditory accuracy returns immediately
auditory map instructed by visual one
older animals will take longer to learn than younger ones