Barn owls

Question 1

Describe experimental recording of owl head movement

Answer 1

Owl placed on platform
Zeroing speaker placed on track, semi-circle around owl
Magnetic coils track head position

Question 2

How are azimuth and elevation recorded experimentally?

Answer 2

2 co-ordinates

Question 3

Accuracy in azimuth and elevation

Answer 3

1-2 degrees

Both ears required for information analysis

Question 4

Sensitivity to sounds

Answer 4

Most sensitive to sounds from front

Sensitive to higher frequencies (1-9kHz for azimuth, 3-9kHz elevation)

Question 5

Effect of plugging ears

Answer 5

Plugging left ear - owl strikes above target
Right - strikes below
Elevation affected more than azimuth
Hard plug more effective than soft

Question 6

Feather types and function on face

Answer 6

Aricular feathers - acoustically transparent

Reflector feathers - underneath aricular

Question 7

Face structure under aricular feathers

Answer 7

Trough around bottom of face, channels sound into ears.

Question 8

Ear locations

Answer 8

Asymmetrical. Eyes, however, are even
Left ear sits above line of eyes (pointed down)
Right ear sits below line of eyes (pointed up)

Question 9

How does the trough accommodate the eyes pointing different ways?

Answer 9

Trough for left ear also points down, trough for right point up
Helps direct sound more effectively

Question 10

Physiological effect of plugging ears

Answer 10

Plugging right ear focuses more sound into left ear, making the owl think the target it below, rather than above
Owl is using inter-aural intensity differences to determine elevation

Question 11

The reason for the small difference on localisation in azimuth when ears are plugged

Answer 11

Interaural level difference (intensity) and interaural time difference (time)
Ongoing disparity determines azimuth
Head turns in azimuth guided by disparities of a few microseconds

Question 12

How does the owl acheive analysis of ILD and ITD

Answer 12

Frequency analysis in inner ear done by auditory nerve, each fiber encoding different freq
Each fiber encodes time AND intensity

Question 13

How can sensory neurones in the ear encode both timing and intensity?

Answer 13

Intensity encoded by rate of APs

Timing encoded by phase locking

Question 14

Describe phase locking

Answer 14

Each fibre fires at a particular phase angle of the sinusoidal input signal

Question 15

What cues are used to estimate distance?

Answer 15

Signal specific: amplitude of sound, frequency spec of sound, amplitude of reverberation
Location specific: off-axis reflection and near-axis reflection. Elevation of direct sound

Question 16

How could you show parallel processing was occuring neuronally?

Answer 16

Record external nucleus (informs optic tectum) and inject anasthetic

Question 17

General neuronal pathway

Answer 17

Acoustic stimuli processed on basilar membrane

Sent via cranial nerve 8 to cochlear nuclei

Question 18

Arrangement of neurones in ICX

Answer 18

Space-specific neurones arranged in orderly topographic sequence, forming a map of auditory space in ICX

Question 19

How is the difference in the timing of information reaching the coincidence detector rectified?

Answer 19

Delay line acts to synchronise input signals so they strongly activate the coincidence detector

Question 20

How does a coincidence detector function?

Answer 20

Fires maximally when it received input from both elements