Bat echolocation and barn owl hearing

Question 1

What is biosonar?

Answer 1

An image-forming system using reflected sound

Question 2

What is the function of nose leaves?

Answer 2

To funnel sound into a cone in a specific direction

Question 3

What is echolocation used to detect?

Answer 3

Distance and amplitude (for size)
Direction; elevation and azimuth (horizon)
Velocity (using the Doppler shift)

Question 4

What are the two main types of ultrasonic signals?

Answer 4

Frequency modulated and constant frequency pulses

CF pulses are short and only at one frequency

Question 5

Give an advantage and a disadvantage for frequency modulated pulses?

Answer 5

Provide an accurate target distance but due to the fact that it is spread out it, it doesn’t travel as far as CF

Question 6

What is the Doppler Shift?

Answer 6

An alteration of sound frequency when the source moves relative to the reciever
The speed of the moving object adds to the speed of the sound causing shorter wavelength and higher pitch when it is approaching the subject

Question 7

How do bats use the Doppler shift?

Answer 7

When they emit sounds, if an echo returns at a high frequency a bat will know that it is approaching the target
They also use flutter analysis, taking advantage of the acoustic glints emitted by wing beats

Question 8

What happens if an echo isn’t within the acoustic fovea?

Answer 8

Adapts the frequency of their calls

Question 9

What is the neural pathway from the ear to the auditory cortex?

Answer 9

Ear -> auditory nerve -> cochlear nucleus -> midbrain inferior colliculus -> forebrain auditory cortex

Question 10

What are the three main areas of the auditory cortex in bats?

Answer 10

FM-FM (Velocity coding)
CF-CF (Distance coding)
Both only fire when there is a call AND echo
DSCF

Question 11

How do bats in colonies avoid cross talk?

Answer 11

The fundamental call has a very low amount of energy and is transmitted to the bat’s inner ear via skull tissue
This means that only that bad will hear the fundamental call and its corresponding echo, the other bats will only hear the echo so their neurons won’t fire

Question 12

What behavioural tests showed that owls use sound to target their prey?

Answer 12

Owls strike at a mouse in rustling leaves
Owls strike at rustling paper tied a distance away from the mouse
Owls strike at speaker hidden in the leaves
Owls make rapid and accurate head movements towards brief sounds

Question 13

What are aricular feathers?

Answer 13

Feathers surrounding the face that are acoustically transparent meaning they let sound pass through

Question 14

What do reflector feathers do?

Answer 14

Deflect sound into the ear

Question 15

Describe the ears of owls

Answer 15

Asymmetrically positioned, the right ear is slightly below the eyeline and points upwards while the left is slightly above and points downwards
The trough on each side points the same way as the ear

Question 16

What do owls use to determine the elevation and azimuth of a target?

Answer 16

Elevation = Interaural level difference
Azimuth = Interaural time difference (interaural disparity)

Question 17

How are the intensity and timing encoded by the sensory neurons?

Answer 17

The greater the intensity the greater the rate of action potentials
Timing is encoded by phase locking; each fibre only fires at a particular phase angle on the sinusoidal input signal

Question 18

What is the cochlear nucleus made up of?

Answer 18

Angular nucleus

Magnocellular nucleus

Question 19

What is the infereior colliculus made of?

Answer 19

External nucleus
Lateral shell
Core

Question 20

After diverging in the auditory nerve, where does the information for time and intensity converge again?

Answer 20

Lateral shell

Question 21

What tests show that parallel processing occurs in the ear?

Answer 21

Lesions in the magnocellular nucleus lead to an inability to accurately detect a target on the azimuth
Lesions in the angular nucleus has the same effect with elevation

Question 22

Who proposed the model for coincidence detection?

Answer 22

Lloyd Jefferess (1948)

Question 23

How does coincidence detection work?

Answer 23

The coincidence detector gets signals from both ears. If both signals come at the same time there is a strong output from the detector but a time delay leads to weak impulses.
The faster side is slowed by an adjustable delay line to cause coincident signals to form

Question 24

What is phase ambiguity?

Answer 24

When there are two sounds which are exactly one cycle apart

Question 25

Where and how is phase ambiguity overcome?

Answer 25

At the position of the inferior colliculus and because each cell is specific to only one combination of time delay and elevation

Question 26

What type of map does the owl auditory system use?

Answer 26

Computational

Question 27

What are the advantages of maps?

Answer 27

Quick

Simplifies processing

Question 28

What is frequency convergence?

Answer 28

The brain finding overlap of frequencies to reduce phase ambiguity