Bats

Question 1

What is biosonar?

Answer 1

Image-forming system using sound instead of light

Question 2

Two major sub-orders of bats

Answer 2

Megachiroptera (egyptian fruit bat)

Microchiroptera (horseshoe bat)

Question 3

First clue to echolocation

Answer 3

Spallanzani and Jurine 1794, blind bats still avoided obstacles

Question 4

Griffin and Pierce ‘38

Answer 4

Instrument detected high frequency signals

Plugging ears or taping mouth prevents navigation

Question 5

How is distance and size calculated from an echo?

Answer 5

Time-delay of echo and amplitude

Question 6

How is elevation assessed?

Answer 6

Move ears independently to compare amplitude

Question 7

Two types of ultrasonic signals

Answer 7

Frequency modulated (drops from high to low, big brown bat)
Constant frequency  (horseshoe bat, small FM component

Question 8

How does echo change as bat approaches target?

Answer 8

Frequency increases

Amplitude decreases

Question 9

What is a`harmonic?

Answer 9

Integer multiple of the call (call at 20kHz produces 40 and 60kHz echo)

Question 10

Info from frequency modulated calls

Answer 10

Each echo of varying frequency given info on

Question 11

Info from constant frequency calls

Answer 11

Target velocity, insect wing beat, one frequency which propagates further (uses doppler shift)

Question 12

Describe doppler shift use

Answer 12

Speed of object adds to speed of sound to produce higher pitch
If echo returns at higher freq, target is approaching bat (same frequency if stationary)

Question 13

Wing beat analysis

Answer 13

Wing moving toward bat will produce doppler effect

Frequency and amplitude of echo modulates as angle of wings change (angle is species specific)

Question 14

Why CF signals useful for doppler shift analysis

Answer 14

Need to compare freq of call to echo for DS analysis
CF have more energy for more range
CF bats sensitive to narrow freq range around CF component of call (acoustic fovea)

Question 15

Whys is acoustic fovea focused at higher freq than cell?

Answer 15

Returning echo often higher freq

lowers voice so echo returns within AF - DS compensation

Question 16

Exclusively FM
Predominantly CF
Combined
(uses)

Answer 16

High frequencies reduce background clutter
(search phase) - often from exposed perch. Greater distance. Lower freq to propagate further
Accurate target distance and flutter

Question 17

Ear characteristics of bats

Answer 17

Enlarged for faint echoes

Specialised flap - pinnae

Question 18

Peripheral mechanisms

Answer 18

Pinnae help funnel sound into cone rather than sphere (sound width moderated by altering nose leaf
Pinna designed for directional selectivity to frequencies

Question 19

Ear specialisation

Answer 19

Outer ear contains pinnae (design dictates freq specialisation)
Middle ear - transmitted via ossicles
Inner ear - oval window to cochlea containing basilar membrane hair cells

Question 20

Neural structure

Answer 20

Ear
Auditory nerve to (hindbrain) cochlear nucleus
(Midbrain) inferior colliculus
(Forebrain) auditory cortex

Question 21

Process in basilar membrane (in cochlea)

Answer 21

Sound waves come through inner ear into canal
Vibrating of drug stimulates hair cells which excite primary auditory neurones
Specific freq will excite specific part of basilar membrane

Question 22

Processing in inferior colliculus

Answer 22

Has interneurons sensitive to call-echo delays
Tells about distance
Many neurones around call freq

Question 23

FM-FM area of auditory cortex used for

Answer 23

Distance coding (neurones respond to delay between call and echo)
Each neurone tuned to particular delay and amplitude

Question 24

CF-CF area used for

Answer 24

Responding to CF call and echo in combination

Encode specific velocities

Question 25

Character of DF-CF area

Answer 25

30% volume of auditory cortex
Frequency species specific
Analyses type of target

Question 26

Overcoming cross talk

Answer 26

Energy in call (fundamental harmonic) <1%

Others only hear higher harmonics

Question 27

How don’t bats deafen themselves?

Answer 27

FM species contract inner ear muscles

CF - call lower than echo. Echo kept in fovea by compensation so call falls outside fovea