How Hearing Guides Action

Question 1

BATS (CHIROPTERA)

Answer 1

MEGACHIROPTERA
-150 species; roost in caves
- large eyes; simple ears
- non-echolocating; clicking (HF; short; frequent pulses)
MICROCHIROPTERA
- 800 species
- small
- small eyes
- complex ears
- echolocation

Question 2

BASIC BAT STUDIES

Answer 2

SPALLANZANI (1794); JURIN (1795)
- hearing = essential for bats to avoid obstactles in flight
GRIFFIN & PIERCE (1938)
- emission of high-frequency ultrasonic pulses in flying bats
ALCOCK (2007)
- ultrasound attenuates quickly; useful for short-distance object detection/tracking

Question 3

BAT ECHO

Answer 3

• echo variation = direction/delay/amplitude/frequency
• factors = physical (wave propagation/diffraction); object range/size/distance/velocity

Question 4

NEUWEILER (2003)

Answer 4

CF/FM ECHOLOCATION
- horseshoe/moustached bat
- usually forage close/within dense vegetation; longer time
FM ECHOLOCATION
- most insectivorous bats
- usually when approaching prey target
CLICK-LIKE ECHOLOCATION
- gleaning/flower-visiting bats
- pick up prey from substrates/forage on flowers; less intense (aka. whispering)

Question 5

HARMONICS IN BAT VOCALISATION

Answer 5

• natural sounds aren’t pure tones; can be harmonics/overtones
• sounds produced by instruments/singing birds/vocalising bats contain harmonics; harmonic frequencies = multiples of fundamental frequency
• greater horseshoe bat: broadcast frequency = 2nd harmonic (loudest frequency band); preferred = around 83kHz

Question 6

CF SIGNALS

Answer 6

• constant frequency
• narrow band
• excellent for analysis of object movement/detection over long range
• long pulses
• higher energy

Question 7

FM SIGNALS

Answer 7

• broadband
• excellent for distance/texture analysis

Question 8

CAREW (2000)

Answer 8

• what info does a bat require to locate/identify prey?
  1. distance to object
  2. size of object (loudness/amplitude of acho = subtended angle)
  3. object location
  4. moving (doppler shift)/stationary
  5. object texture

Question 9

CAREW (2005)

Answer 9

• how well can bats discriminate dif sources?
• training = near platform contains reward; far doesn’t; sides swapped regularly
• tests = sound-reflective targets removed from platforms; replaced w/speakers; phantom targets presented via loudspeakers when pulse-echo delays = modified & simulate smaller distances between targets until choice performance breaks down (random choices around 50%)

Question 10

SIMMONS (1971; 1973)

Answer 10

• distance estimation from delay between pulse/echo
• spatial acuity differs between CF/FM bats

Question 11

WEBSTER & GRIFFIN (1962)

Answer 11

• echolocation phases during approach
• myotis lucifugus (little brown bat) capturing mealworm tossed into air
• neural basis of echoes:
  eardrum -> basilar membrane -> cochlea -> semicircular canal -> cochlear nucleus -> auditory cortex

Question 12

AUDITORY INTERNEURONS

Answer 12

• selectively tuned to preferred frequencies
• little brown bat = FM; aka. no preferred freuqency
• horseshoe/mustached bat = CF/FM

Question 13

ACOUSTIC FOVEA IN CF BATS

Answer 13

• rhinopholus
• first-order auditory neurons = auditory nerve
• second-order auditory neurons = cochlear nucleus
• fovea for fine-frequency analysis = more neurons & sharper tuning

Question 14

SUGA (1990)

Answer 14

• parallel pathways process dif features of biosonar info in CF/FM bats
• info processing = segregated/coded in parallel pathways early on
• target velocity = computed from comparison of frequency shift in CF component between pulse/echo (due to Doppler effect); comparison involves dif frequency bands (fundamental up to 3 harmonics)
• FM component allows to compute distance from time delay between pulse/echo; also done across freq bands

Question 15

AUDITORY CORTEX IN MUSTACHED BAT (PTERONOTUS PARNELLII)

Answer 15

• cells respond be to FM1/FMx
• corresponds to target range (7-310cm)
• max neurons = 50-140cm
• cells respond to CF1/CF3 for velocity
• CF area = modulation-sensitive neurons aka. Doppler effect induced by movement

Question 16

CATANIA & KAAS (1996)

Answer 16

• sensory maps exist in vertebrate/invertebrate brains
• 3 somatosensory maps in cortex of star-nosed mole w/subdivided areas for dif tips of star-nose aka. touch organ
• nose w/22 fleshy rays & lots of Eimer’s organs; ray11 on each nose side = short/more sensitive w/largest projection area in somatosensory map

Question 17

SUMMARY (1)

Answer 17

• sensory info = filtered/modified/amplified at dif stages of serial sensory processing
• parallel processing = implemented in sensory pathways (ie. P/M pathways in primate/human vision; ILD/ITD coding in mammalian/bird hearing; velocity/range coding in bat auditory pathways)
• spatial segregation/co-localisation of neurons w/similar function that systematically connect to another neuron pop (neural map) = fundamental feature in organisation of brain areas/pathways

Question 18

SUMMARY (2)

Answer 18

• preservation of spatial locations of sensory sources in outer world via topological sensory maps in brain (directly as retinotopic mapping in visual pathways/indirectly by reconstructed spatial maps in auditory pathways (ie. owl’s spatio-tonotopic map in MLD))
• highly ordered organisation of feature-extracting interneurons as sensory maps found in mammals/birds/insects (ie. mammalian V1/somatosensory cortex/star-nose mole somatosensory map/bat primary auditory cortex/owl ICC/insect central body)