Bat Echolocation Flashcards
What did Lazzaro find about bats?
- producing sound and being able to hear is vital for navigating
- removed eyes = fine
- plugged ears = not fine
- tubes in ears = fine
- plugged tubes in ears = not fine
- tapped mouths shut = not fine
What did Griffin find about bats?
- animal rights activist
- using theory determined that they use ultrasound and coined the term echolocation
- used an ultrasound detector made by Peterson
- discovered that bats hit or touched a wire more if it was thinner (<0.5mm)
- as bats got closer to target their pulse rate increased and pulse duration decreased
What did Simmons find about bats?
- use delay between pulse and echo
- trained bats to land on one of two platforms
- used speakers to play back a phantom echo
What are the two components of the emitted ultrasound? What environment is each useful in?
- Frequency modulated (FM) component: useful in forests
- Constant frequency (CF) component: useful in open spaces
What kind of bat is Eptesicus?
- FM bat
- produce broad band signal 100 khz to 25 khz
How is distance deciphered?
- use time delay from pulse to echo
- FM bats use frequency analysis and time analysis
- echo intensity: far away if weak
- frequencies returned: high frequencies don’t travel far
How is the subtended angle deciphered?
- the loudness of the echo determines the subtended angle
- problem: could be small and close or far away and large
How is absolute size deciphered?
- using a combination of distance info (delay) and subtended angle (amplitude)
What does a azimuth angle tell the bats and how is it found?
- location in the horizontal plane
- by binaural cues
What does elevation tell the bats and how is it found?
- location in vertical plane
- moving ears in various positions
What kind of bat is rhinolophus?
- CF-FM bat
- pulses with long constant frequency then rapid downward FM sweep
- sensitive to 83 KHz
What is the doppler shift problem?
- if the predator and prey are still, the frequency will return the same
- if predator and prey are moving towards each other, the frequency will increase
- problem: returning frequency could be outside of species specific frequency range
How do bats compensate for the doppler shift problem? What research was done to discover this?
- when moving forward they lower the frequency emitted so the returning frequency will be within the specific range
- bats placed on swing and recorded pulses
- also means that the loud pulse emitted is out of their range and they avoid deafening
What is the acoustic fovea?
- increase in sensitivity to a narrow range of frequencies
- results from a range of adaptations
What kind of bat is Pteronotus?
- CF-FM bat with several harmonics
- harmonic at 60 Hz is the loudest
What are the pulse and echo also called?
- pulse = noise
- echo = signal
How is velocity determined by the bats?
- analyze the doppler shift echoes to determine if the bat is gaining or not
How is flutter determined?
- position of the wing of prey
- if wing is ‘close’ to bat will produce a higher frequency
- if wing is horizontal there is a smaller surface area for the echo to bounce off of, decrease in amplitude
How does rhinolophus use its different components?
- uses CF component to determine flutter while hanging still
- uses FM component for tracking and capture
What special adaptations do bats have in the outer ear?
- large pinna and tragus which allows them to detect faint echoes
- nose leaves to direct sound coming from nose
What occurs when the human pinna is distorted?
- can no longer differentiate where sound is coming from
What is the structural discontinuity of the basilar membrane?
- abrupt thickening and lengthening where the species specific CF component frequency is cast
- results in expanded region for preferred frequencies and increase in sensory neurons in critical range
- (basilar membrane thins and widens at low frequency end)
How do hair cells work?
- cells are stimulated by the movement of the basilar membrane
- pressure causes them to bend and the tip links pull open K channels
- get K influx that depolarizes the cell
- causes Ca influx
- then K efflux to repolarize
- hair cells don’t generate an action potential, they release NT
What is the hearing threshold? How are bats specialized?
- determines how weak a stimulus can be presented and still be heard
- at species specific frequency they have a low threshold to be able to detect quiet echoes
What is Q10?
- tells us how sharply tuned the auditory neurons are
- the larger the Q10 the more sharply tuned
- tuning curve allows us to calculate Q10
- Q10 = best excitatory frequency/width of V shape 10 db above threshold
How does the inferior colliculus process? Who found this?
- George Pollak
- neurons in inferior colliculus are sensitive to pulse-echo delay
- fire once or twice for pulse and for echo
- increased stimulus does not change firing raes
- important for distance (and velocity)
How does the auditory cortex process sound? Who discovered this?
- Suga by looking at Pteronotus
- FM-FM area: orderly arranged neurons respond to unique combinations of FM component of pulse and echo (distance)
- CF-CF area: sensitive to unique combinations of CF component pulse and echo to encode velocity
How is sound processed specifically in the FM-FM area?
- neurons in this areas respond well to an FM component followed by an FM echo
- three types of delay sensitive neurons; comparison of call FM1 to pulse FM2, FM3, FM4
Where does the FM-FM area get its input from?
- from different groups in the inferior colliculus tuned to FM1, FM2, FM3 or FM4
- inferior colliculus - medial geniculate nucleus - cortex
Why is the neural response to FM1 pulse delayed?
- FM1 pulse delayed at medial geniculate nucleus but response to echo is not
- because MGN neurons are coincidence detectors that respond to certain pulse-echo delay
How is sound processed specifically in the CF CF component?
- CF1-CF2 and CF1-CF3 neurons respond to combination of tones
- preferred CF1 frequency increases along one axis
- frequencies of harmonics increase along right angles of CF1 axis
- creates a dual frequency coordinate system meaning a specific location represents a target velocity
How does the DSCF area process sound?
- code for certain frequencies and amplitudes of echoes specifically doppler shifted CF2 signals
- respond to echo regardless of pulse
- cortical part of acoustic fovea
How is the DSCF area arranged?
- columns are arranged radially
- from one column to the next specific amplitude changes
- moving outward along the spoke, the frequency increases
What did Suga find?
- a pharmacological inactivation of the DSCF area resulted in frequency discrimination disruption but not delay disruption
- an inactivation of the FM-FM area resulted in disruption of delay discrimination but not frequency discrimination
What is the reason for using many harmonics?
- allows bats to broaden bandwidth
Why do bats not get confused with one another?
- they are cortically deaf to one another
- cortical neurons need a dual password to fire
