Paul - Mechanisms of Sound Localisation

Question 1

Identify auditory cues for horizontal sound localization

Answer 1

First action in hunting:
Owls responds to a sound with a rapid head flick (saccade) orienting their face directly toward the source.
Stimulus cues used for horizontal sound localization:
Owls (and humans) use inter-aural time differences (ITD - Time difference the sound takes when it travels from one ear to the other) and inter-aural intensity differences (IID - Closer ear to sound source gets stronger signal) to determine the horizontal origin (azimuth) of a sound.

Question 2

Describe an experimental method used to measure sound localization precision

Answer 2

Stimulus:
* Sounds with controlled ITDs
* Delivered via earphones
Measured Response:
* Head orientation (azimuth)
Key Finding:
* Owls oriented towards
perceived sound source
* Response matched natural
sound localization

Question 3

Explain the anatomical adaptations that enable vertical sound localization in barn owls

Answer 3

Owls use inter-aural intensity differences (IID) to
determine the vertical (elevation) location of sound.
Anatomical specialization: asymmetric ears
* Convergent evolution across multiple genera
* Two types:
1. Soft tissue asymmetry (e.g., barn owl)
* Asymmetric skin flaps
* Symmetric skull
2. Skull asymmetry (e.g., boreal owl)
* Asymmetric ear openings in skull

Question 4

Explain the concept of a “topographic map of auditory space in the brain”

Answer 4

ICX neurons exhibit spatial selectivity:
* Respond to sounds from specific
locations in space
Form a neural map of 2D auditory
space
Analogous to somatosensory
topographic maps, but fundamentally
different in origin:
* Somatosensory system: Direct
mapping of touch receptors to
brain regions (inherent spatial
organization, lecture 6)
* Auditory system challenge: No
inherent spatial organization in
cochlea
Brain must compute sound source
location

Question 5

Construct a neural circuit model that processes horizontal sound location information

Answer 5

Sound from directly ahead:
* Reaches both ears simultaneously
* Action potentials coincide at array midpoint
Sound from the right:
* Arrives at right ear first
* Coincidence point shifts along detector array:
* Right CN action potential travels further
* Meets left CN action potential at off-center location