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Flashcards in Hunting and Hearing in Bats Deck (17)
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many well developed senses
communicate by vocalisation
navigate and hunt by echolocation
neurons in mid brain pinpoint prey location
echoes that bounce of large objects will be louder
bats able to distinguish own call from that of others
low light conditions
as relatively little sound energy may be reflected of objects of interest- cries are loud and adjustable
by comparing sound at LR ears can judge object
measuring time can judge distance
discriminate sizes and textures


Intercepting prey

sound made changes on activity
cruising- 10/s usually approach at 1m can detect 5mm prey 3m away
approach- ears and head point at prey, cries 40/s and shorter
interception- cries up to 160/s all distinct FM calls
prey caught near fingers in skin web
loudness decreases with distance
low tones travel further than higher


Frequency modulated calls

short burst of high freq that drops very quickly to low freq part
most produce these
usually high to low


2 issues for the bats brain

1. bat cry very loud- swamps auditory system


measuring cry and echo delay- usually brief

mapped in cry echo neurons
each neuron responds to particular delay


Auditory system

fairly typical mammalian ear
number of muscle attached to small bones can contract very fast to uncouple the bones and reduce sound transmission during cry
cochlea- hair cells- sensory neurons- auditory nerve- cochlear nucleus
sound processed by number of nuclei
major pathway= cochlea nucleus- inferior colliculus- auditory cortex
many pathways as sound diminishes quickly so need to send very quickly to different brain areas in order to process entirety of sound


Major specialisations

less sensitivity to loud sounds
auditory neurons recover quicker than usual
time marking and CE neurons


Time marking neurons in ICX

mark precisely the time of cry and echo
very sensitive
each one prefers particular tone
makes single spike at beginning of sound
different neurons respond to diff freqs so different ones may respond to different parts of fm bursts


Cry-Echo Neurons

do not respond to single CF or FM cries
need loud cry then soft echo with correct delay
each neuron tuned to particular object at particular difference
needs 2 synapses that are activated at same time to be excited as a coincidence detector
spikes initiated by bats own cry are delayed by longer neurons
CE will be excited if cry spike and echo spike reach neuron at the same time


Suga (1980) moustached bat

different areas of brain dedicated to different functions
neurons with similar CE delays in groups in column
preferred delay changes in orderly way- map
delays anterior to posterior
many neurons respond to 0.5-1.4m when approach is initiated- special fovea


Constant Frequency calls

call that remain around one freq
very few species
can pick up flying insects against cluttered background
sound energy concentrated at one tone so CF cry can be louder so travel further- good for hunting in open spaces


Doppler Shift Reaction Compensation

sound tone changes if emitter and listener are moving toward or away from each other
moving toward each successive wave has a shorter distance to travel so receiver hears more waves per s so higher tone
next cry has tone altered to maintain tone of constant echos
many neurons dedicated to tones just higher than CF cry- acoustic fovea
starts in cochlea; turning is sharp so cry itself not so well represented as the echo anti deafening mechanism


Parnells moustached bat

30% of bat cortex dedicated to DSCR


What is the function of the DSCF area?

to detect acoustic glints made by flying insects


Avoiding Jamming

cries often contain several harmonics
1st softer than 2nd
bats do not usually hear the 1st of their neighbours
several auditory cortex neurons respond best to a soft first harmonic followed by an echo of a sond


Schlegal et al (1985)

time marking neurons found in the superior olivary complex (SOC) and the central nucleus of the inferior colliculus (ICC)
• Concluded neurons reacted to interaural differences of stimulus onset time but not to phase difference (ongoing time difference)


Washington & Kanwal (2008)

found that DSCF neurons extract multiple parameters of FMs and are specialized for processing both FMs for communication and CFs for echolocation