Prey Localization by Barn Owls

Question 1

Studying sound localization accuracy in the lab (tools?)

Answer 1

Search coil on head - generates electricity when looking
Target speaker - played noise in any space, owl immediately oriented its head towards it

Question 2

Peripheral features

Answer 2

Facial ruff - helps push sound towards one area (i.e. satellite dish)
Asymmetrical ears - right ear opening is directed upward (sensitive to sound from above), left ear opening is directed downward (sensitive to sound from below)

Question 3

Azimuth

Answer 3

Sound’s place on the x-axis (measured in interaural time difference (ITD))

Question 4

Elevation

Answer 4

Sound’s place on the y-axis (measured in interaural level difference (ILD))

Question 5

How sound localization is determined

Answer 5

Localization has to be computationally extracted (timing - azimuth, intensity - elevation)

Question 6

Experiment to determine contribution of asymmetry of ears to elevation (ILD)

Answer 6

Right ear plugged → owl orients downward, left ear plugged → owl orients upward (orientation more intense w/ hard plug versus soft plug)
Removal of facial ruff also eliminated detecting information about elevation

Question 7

Elements of azimuth (ITD) - different disparities

Answer 7

Temporal disparity - time difference between sound arriving at the two ears
Transient disparity - sound begins & ends sooner in the ear closer to the sound
Ongoing disparity - sound reaching the far ear will be delayed (important for azimuth)

Question 8

Neural pathways for processing sound

Answer 8

Inner ear → cranial nerve VIII → cochlear nuclei in brain stem (Nucleus Angularis (NA) and Nucleus Magnocellularis (NM))

Question 9

Parallel pathways for level & time information

Answer 9

NM from both sides goes to Nucleus Laminaris (NL) - calculates time info from both sides, NA goes to dorsal lateral lemniscus (LLDp) → NL goes to dorsal lateral lemniscus (LLDa) → both sides go to inferior colliculus (ICC) → ICC goes to space-specific neurons (ICx)

Question 10

Physiological evidence for segregated processing of time & level information

Answer 10

NM neurons phase lock (provide info about time difference) but are less sensitive to intensity difference in sound - connected to ITD
NA neurons do not care about phase of sound, but do care about level - connected to ILD

Question 11

Experiment to find evidence for parallel processing of time and intensity

Answer 11

Pharmacological manipulation - effect of lidocaine in NA on ILD tuning in ICx → ILD is affected while ITD isn’t (NA not tuned for phase, only intensity/level)

Question 12

ITD coding in the barn owl - two models

Answer 12

Coincidence detection in the NL
Jeffress’ model: coincidence detectors, delay lines

Question 13

Coincidence detectors

Answer 13

Each neuron is tuned to a specific ITD, selective for different interaural time disparities → conversion from time code to place code (each neuron represents a place, either closer to the left or right ear)
Stimulus meets at one neuron from both ears, different neuron depending on which ear received the stimulus first

Question 14

Delay lines model

Answer 14

Time is added to the neuron that received the stimulus first so both sounds can combine to produce the maximum output

Question 15

Experiment to determine contribution of visual input to sound localization

Answer 15

Changes in sound localization to chronic insertion of ear plugs → gradually learn to correctly locate a sound (potential role of vision)
Ability is lost in adults, young owls recalibrate once ear plugs are removed (can only readjust if vision is intact)

Question 16

Prism experiment - visual control of auditory system

Answer 16

Prism placement - optically shifts a large portion of the visual field 23 degrees along the horizon → alters the normal association between auditory cues and locations in the visual field

Question 17

Experiment that first showed visual calibration of auditory system

Answer 17

Measured head orientation to a visual stimulus or an auditory stimulus (used search coil) → head orientation was plotted relative to true location

Question 18

Critical period for auditory adjustment during prism experience

Answer 18

If prism experience begins after ~70 days, there is no auditory plasticity (cannot readjust)

Question 19

Neurons in the optic tectum respond to both visual and auditory stimuli

Answer 19

Ascending ITD + ILD information → inferior colliculus central nucleus (ICC) → inferior colliculus external nucleus (ICx) - auditory space map → optic tectum (OT) - multimodal space map (also receives visual input from retina and forebrain)