Bat Echolocation

Question 1

Why ultrasound

Answer 1

good for small objects

Question 2

disadvantages of ultrasound

Answer 2

strong attenuation, limit range, so need to do louder/longer calls

Question 3

Discovery of ultrasound and how calls affected by search

Answer 3

Griffin, higher rate/shorter duration as approach target, search/approach/terminal

Question 4

Two (3) types of call

Answer 4

FM = freq.modulated, broadband.
CF = constant.freq, narrowband
CF-FM = both

Question 5

Describe FM signals

Answer 5

short <5ms, quickly sweep down range of freqs, harmonics

Question 6

Describe CF signals

Answer 6

Longer 30ms, narrowband

Question 7

Distance estimation

Answer 7

FM signal Delay time of pulse-echo, can do within 10-15mm 75% accuracy threshold

Question 8

Acuity of echo delay

Answer 8

Jitter experiment, good to 10ns, enough of 2um in target = acoustic texture, moth from wall

Question 9

Why FM for distance

Answer 9

Broadband gives good range for time delay across points

Question 10

Angular Size?/absolute

Answer 10

Amplitude/loudness
Get absolute size from distance (delay) + subtended angle (loudness)

Question 11

Location cues?

Answer 11

Azimuth by using interaural timing, elevation by interaural intensity

Question 12

How doppler shift works

Answer 12

If approach stationary = higher freq
Receding = lower freq
appraoching object = higher freq

Question 13

Doppler shfit analysis (what 2 things analyze about target used for) mustached bat

Answer 13

Use CF signal since constant, good analysis
USE TO DETERMINE VELOCITY
Doppler shift compensate to KEEP ECHO IN ACOUSTIC FOVEA
Used fo FLUTTER DETECTION ALSO, doppler echo of flapping wings of insect (+/- 30Hz wow!, 0.04% change in freq heard)

Question 14

FM vs CF

Answer 14

FM - broadband good for hunting on ground with vegetation, good for texture/distance
CF - narrowband, good for open fields, doppler shift/velocity/flutter

Question 15

Explain harmonics of mustached bat CF-FM

Answer 15

2nd harmonic at 61kh is loudest, this is where their acoustic fovea is
1st harmonic is softest bc only they can hear it (allow for combo sensitive neurons to fire only for their calls/echos)

Question 16

Adaptations of CF-FM mustached bat aud system

Answer 16

Acoustic fovea over-rep. of neurons for CF component of call
During doppler compensation they reduce sensitivity to loud call so can hear quiet echo

Question 17

Describe q10db factor

Answer 17

Quality factor, how sharply tuned the neurons are
Display frequency and dB threshold graph, see char freq. point and go up 10Db, HOW WIDE IS the factor, higher factors are better weirdly
Most common in CF bats, FM bats don’t have as good sharp tuning since broadband

Question 18

Bats and aud sensititvity HOW DO IT

Answer 18

Reduce sensitivity DURING call, so that they are ready to hear the soft echo

FM bats - contact middle ears to attenuate loudness
CF bats - cant contract since freq overlap, so call is LOWER then doppler echo, ECHO FALLS ON FOVEA, CALL DOESN’T

Question 19

Aud Path in bats

Answer 19

Cochlear nucles - sup. olive - lateral lemniscus - Inferior colliculus - Medial geniculate nucleus - Aud cortex

Question 20

Post-stimulus time histogram what show

Answer 20

Time from onset of stim and then neurons firing,
Louder sound = shorter latency
EXCEPT IC NEURONS - accurately encode pulse-echo delay so fire without wavering when hear sound even if louder no jitter
USE IC NEURONS FOR DISTANCE ESTIMATION

Question 21

IC neurons

Answer 21

Accurately encode pulse-echo delay
Low spiking threshold sharply tuned to a freq. in an FM sweep
Respond to pulse-echo pair of particular delay

Question 22

FM-FM area

Answer 22

axis for delay in vert columns and axis for harmonic pairing (FM1 to FM2/3/4),
Map of delay, Tuned to DELAY AND AMPLITUDE (respond only to soft echoes)
ENCODE SIZE (loudness/delay) AND DISTANCE
FM1 Pulse is actively SLOWED to reach MGN coincidence with echo at SAME TIME
columnar organization duh

Question 23

CF-CF area

Answer 23

Encode velocity
Respond only with pulse and doppler echo, combination sensitive
Axis for Delay time and axis for pairs (CF1 to CF2/3), overlap so allow compute velocity

Question 24

Doppler shifted CF area (DSCF)

Answer 24

Process doppler shifted CF calls
sharply tuned around 61khz
Tuned to FREQ AND AMPLITUDE OF ECHO, NOT CALL, acoustic fovea
columnar too, particular CF and amplitude axes

Question 25

Parallel processing

Answer 25

All of this computation is happening in parallel, freqs segregated in IC
Combined in MGN for coincidence stuff

Question 26

Why not just emit one harmonic

Answer 26

1st harmonic is weakest so other bats don’t use it for their combos
Dont get confused with other bat calls
Need 1st harmonic for combo sensitive
FM-FM/CF-CF NEURONS DONT RESPOND TO HIGHER HARMONIC PAIRS - NEED 1ST HARMONIC for the paired signals