Barn Owl Prey Localization

What are 2 points about barn owls

• Barn owls are nocturnal and hunt small prey (voles, mice, frogs, small birds).

• They can accurately locate and strike prey in complete darkness, relying heavily on auditory cues.

How does Mechanotransduction in Hearing work

• Stereocilia on hair cells move in response to sound waves.

• Movement opens mechanoelectrical transducer (MET) channels:

  • Ultrafast response (microseconds).

  • No second messenger system; purely mechanical.

  • Rapid adaptation allows phase-locking up to 2 kHz.

Sound Localization: Two Critical Dimensions:

1. Azimuth (horizontal plane) – Where the sound is left vs right.

2. Elevation (vertical plane) – Where the sound is up vs down.

Accuracy:

• Barn owls can localize sounds with 1º–2º precision between 1–9 kHz.

What are the 2 Auditory Cues for Localization

1. Interaural Time Difference (ITD):

• Timing difference between when sound reaches each ear.

• Used to determine azimuth (horizontal location).

• Two types:

  • Transient disparity – Onset difference.

  • Ongoing disparity – Continuous timing offset in sound waves.

2. Interaural Level Difference (ILD):

• Intensity difference between ears.

• Used to determine elevation (vertical location).

Benefits of Asymmetrical Ears (3)

• Right ear: Faces upward, more sensitive to above.

• Left ear: Faces downward, more sensitive to below.

• The facial ruff reflects and amplifies sound, aiding localization.

Auditory Brain Pathways

• Nucleus Magnocellularis (NM) – Processes timing (ITD).

• Nucleus Angularis (NA) – Processes intensity (ILD).

• Nucleus Laminaris (NL) – Acts as coincidence detector for ITDs.

What is temporal disparity and why is it used

• the difference in the time of arrival of the sound between the two ears

• Used to determine azimuth

What are the 5 Steps in Sound Localization:

1. Sound Detection in the Cochlea

   • Sound waves are converted into neural signals by hair cells.

   • These signals are sent via the auditory nerve to the brainstem.

2. Signal Splits into Two Parallel Pathways

a) Timing Pathway (for Azimuth):

• Auditory nerve → Nucleus Magnocellularis (NM)

  • Processes precise timing of sound.

• NM → Nucleus Laminaris (NL)

  • Acts as a coincidence detector.

  • Compares inputs from both ears to calculate interaural time differences (ITDs).

b) Intensity Pathway (for Elevation):

• Auditory nerve → Nucleus Angularis (NA)

  • Processes sound intensity.

  • Computes interaural level differences (ILDs).

3. Integration in the Inferior Colliculus (ICX)

• NL and NA both project to the External Nucleus of the Inferior Colliculus (ICX).

• Neurons here are space-specific:

  • Respond to specific combinations of ITD and ILD.

  • Are organized in a topographic map of auditory space.

4. Auditory Map is Passed to the Optic Tectum

• The ICX projects to the optic tectum, where auditory and visual maps align.

• This allows the owl to orient its head and eyes precisely toward the sound source.

5. Motor Output

• Visual-auditory integration guides motor commands for head and body orientation toward the prey.

Jeffress Model of ITD Detection

• Proposed by Lloyd Jeffress (1948).

• ITDs are detected using:

  • Coincidence detectors: Neurons that fire when inputs from both ears arrive simultaneously.

  • Delay lines: Axons of different lengths slow input from one ear to match timing.

Space-Specific Neurons in the Inferior Colliculus (ICX): (4)

• Neuron’s respond to specific combinations of ITD and ILD.

• Organized topographically – Each neuron codes for a particular location in space.

• Binaural: Not activated by just one ear.

• Lesions in ICX affect spatial hearing in predictable ways.

Optic Tectum: (2)

• Contains multimodal neurons that respond to auditory and visual stimuli.

• Visual and auditory receptive fields overlap.

Plasticity in Juvenile Owls:

• Visual system “instructs” the auditory system.

• If raised with prismatic glasses (displacing visual field), auditory localization adapts to match.

• This plasticity is limited to a critical developmental period.

  • Depends on visual experience.

  • Involves changes in NMDA and AMPA receptor expression.

What are 2 Key Experiments and Researchers

• Knudsen & Konishi: Showed owls use intensity and timing cues.

• Eric Knudsen (2002, Nature):

  • Demonstrated instructed learning in auditory localization.

  • Visual calibration reshapes auditory spatial maps in the ICX.