Lecture 5 + 6: Muessel: Echolocation in Owls

Question 1

Why do owls use echolocation?

Answer 1

Live in darkness, use echolocation to locate prey in terms of azimuth and elevation based on sound. Have a 75% kill rate.

Question 2

As owls can’t turn their eyes what do they do instead?

Answer 2

Rapid accurate turns of their head. Proven by experiment with a speaker on a rail -change elevation and azimuth of stimulus sound and track head position with search and inducation coils -accuracy of +/- 1 or 2 degrees in terms of azimuth and elevation.

Question 3

How sensitive are owls to sound?

Answer 3

More sensitive to sounds in front and to high frequencies (1,000-9,000 Hz) but range (100-12,000 Hz)

Question 4

What has experiments such as ear plugging showed us?

Answer 4

Both ears are required for accurate locating - Left ear plugged –> looks too high and slightly right - Right ear plugged –> looks too low and slightly left Suggests left = sensitive to sounds below Suggest right = sensitive to sounds above

Question 5

What peripheral mechanisms does the owl possess to aid its echolocation?

Answer 5

Auricular feather- sounds will pass through instead of being absorbed Reflector feathers behind auricular feathers which are dense and ramified in order to funnel sounds into ears Facial ruff- trough at bottom of face in order to funnel the sound up to ears Asymmetric ears - right ear positioned below and tilted upwards, left ear positioned above and tilted down.

Question 6

Why does an owl measure the intensity of sounds?

Answer 6

Uses interaural level difference to determine elevation and help determine azimuth of a sound.

Question 7

What it interaural time difference?

Answer 7

The disparity in time between the sound reaching each ear. This depends on the azimuth of the sound as from one side it will have an increased distance to travel to the opposite ear. Measure the ongoing disparity (up to ms) between frequency markers to determine azimuth.

Question 8

How is the information analysed?

Answer 8

Auditory nerve: - Frequency analysis occurs in the inner ear - Interaural level and time differences are carried into the brain.

Question 9

How is the interaural level difference analysed?

Answer 9

Differences in the rate of action potentials - Determine elevation

Question 10

How is the interaural time difference analysed?

Answer 10

Encoded by phase locking. Nerve fibres fire at a particular angle of sin wave - Not affected by intensity.

Question 11

What do owls use for perception?

Answer 11

Cues: signal and location specific Perceive distance: 20cm accuracy over 2m (10%)

Question 12

How are signal specific cues used in perception?

Answer 12

Using prior knowledge to identify species Overall amplitude and frequency of the sound and reverbaration

Question 13

How are location specific cues used in perception?

Answer 13

Knowledge of environment rather than prior knowledge of sound. Near-axis (Direct) and off-axis (indirect) sound reflection used to determine elevation.

Question 14

What neuronal pathways are used in echolocation by owls?

Answer 14

Inner ear –> auditory nerve –> collaterals –>parellel processing by magnocellular or angular nucleus

Question 15

What does the magnocellular nucleus do?

Answer 15

Analyses timing information Magnocellular nucleus Passed into laminar nucleus –> anterior lateral lemniscal nucleus –> Core The Interaural time difference is then analysed

Question 16

What does the angular nucleus do?

Answer 16

Analyses intensity information Angular nucleus –> Posterior lateral lemniscal nucleus The interaural level difference is then analysed

Question 17

Where do the core and posterior lateral lemniscal nucleus converge?

Answer 17

They converge at the lateral shell Information is then carried to the external nucleus and then the optic tectum.

Question 18

What is the purpose of the external nucleus and optic tectum?

Answer 18

External nucleus: computes map of auditory space, removes phase ambiguity Optic tectum: information from eyes is then incorporated.

Question 19

How is the interaural time difference analysed?

Answer 19

Coincidence detection. Maximal output when input from left and right ear converge at the same time. A delay line can be used to synchronise the input in order to produce a stronger output.

Output place code is a location of the noise in terms of azimuth. This is because each coincidence detector differes in place in neuronal circuit which is mapped somatotopically.

Great the angle the further along the delay line the sound will have to travel before maximal output

Question 20

How do you analyse the Interaural level difference?

Answer 20

Neurons in the lateral lemniscal nucleus are arranged in order.

Ventral / dorsal neurons fire when that respective ear is stimulated most loudly

Question 21

What is phase ambiguity?

Answer 21

Responds maximally to a stimulus because it as an integer multiple

This is prevented by the external nucleus by checking where all the information summates to produce a place code

Question 22

How is the final location decided?

Answer 22

Specific combination of ILD and ITD to produce one location / receptive field

Single neuron location

10,000 neurons are arranged as a topographic sequence which maps out external space

Auditory fovea is located in front of owl so there is a greater location of neurons

Question 23

What type of maps are used by owls to deterime specific locations.

Answer 23

Barn owls use a computational map which represents information as a place code.

Rapid processing as map is already present

Simple connections which are finely tuned.