Auditory Physiology & Behaviour Flashcards
The link between behavior and sensorimotor systems
Behavioral interactions are driven by motor systems, whose commanded output is shaped by the sensory input the organism receives
Acoustic sounds
Airborne sound is produced when a vibrating object sets particles of air in motion, producing a longitudinal pressure wave of alternating compression and rarefaction.
Particles oscillate around a stationary point
Ears sense pressure wave or particle velocity
Velocity sensitive ears (atypanic)
Plumose antennae
- Vibration is sensed by stretch receptors at the base of the antenna
Example: male mosquitoes
- can match resonant freq to female wingbeat freq (allows species and sex recognition)
Discrete mechanoreceptive hair sensilla
- Many Athropods use these in a similair way
Pressure sensitive ears (Tympanic)
Arthropods
- tympanal membrane backed by air-filled tracheal sac (internal pressure reference)
- allows you to detect pressure difference across the membrane
- Chordotonal organ = stretch receptor that detects pressure difference
Mammals
- Tympanal ears more complex in mammals than insects as Tympanal coupled to fluid-filled inner ears
- Challenging to enterpret pressure difference between air and water (water has higher impedance)
- SOlution: The middle ear provides impedance conversion by applying the force communicated from the tympanum to the the oval window, via the lever mechanism of the ear ossicles
- This sets basillar membrane in motion
Basillar membrane mechano- transduction:
1) sounds sends wave along basillar membrane
2) Different frequencies of sound excite the greatest motion at different points along the basilar membrane (tonotopic representation)
3) Oscillations of basilar membrane transduced by inner “hair” cells (not actual hairs) which deflect and change Ca2+ ion channel conformation + open them causes action potential
ionotropic transduction: ion channels are gated directly by the stimulus
- ionotropic = v fast gating (opposite of metabotropic transduction)
Insects use ionotropic transduction to sense the motion of their tympanum
Localising sound
Mechanistically:
-> horizontal: inter-aural differences in timing and intensity (sound from one side of head travels further to reach far ear so is delayed in arrival and attenuated in intensity)
-> vertically: Spectral filtering (differential reduction in sound energy / freq depending on the material it has passed through - head, ears, shoulders)
Neurologically
-> Delay line: The delay is measured by detecting coincident arrival of action potentials from near ear and far ear (delay line), in a form of parallel processing
Aural delay is too short to be measure directly in small mammals where ears are nearer.
example: localisation of males by female crickets
- Sounds can hit the tympanum externally (from ear) or internally (from trachea)
- Phase delays introduced by an elastic membrane (acoustic septum) mean that ipsilateral sounds (sound on near side) at the frequencies at which the males sing produce constructive interference at the tympanum, whereas contralateral sounds (sounds on far side) produce destructive interference.
- Makes each ear very sensitive to sounds on its own side at a specific frequency.
Echolocation
functions by measuring time delay of emission call and receipt of its echo to estimate distance to a surface
frequency
- Calls v high freq as this means short wavelength which is better as is smaller than target
- High freq sounds attenuate (lose amplitude) faster so only good for short distances (trade off)
Duration
- Duration gets smaller as bat approaches prey to acoid call-echo overlap
Mechanism
- Different interneurons are matched to different delays and to different frequencies
- enables fast parallel processing to identify the echo delay at a given call frequency.
Different call designs
1) Broadband calls
- Many changes in frequency so excite freq-specific interneuron briefly
- Benefits: accurate localisation, target discrimination and classification due to precise call-echo matching
(often in terminal buzz)
- Limitation: not good for weak echoes from long distance as only excite freq-specific interneuron briefly
- Use: terminal buzz and cluttered environments
2) Narrowband calls
- Little change in frequency so excite same auditory neuron over longer period
- Benefits: good for weak echoes at long distance, detecting acoustic glints (short peaks in echo amplitude when insect wing perpendicular to wave)
- Limitation: poor for localisation as distance estimate requires accurate freq-matching of a call to its own echo
- Use: open habitats (e.g. species that hunt at alititude -> noctule Nyctalus noctula)
3) Constant freq calls
- Similar to narrowband with frequncy variation at the start and end
- Allows compensation for Doppler shift in freq experience in forward flight – allows call freq to match acoustic fovea (neurons sensitive to specific freq)
- Example: Rhinolophus ferrumequinum
ecological variation (habitat clutter) predicts echolocation signal type, both within and between species.
-> convergent evo of call types in similar habitats
Antipredator defences in moths
Stealth:
- Thoracic scales – absorbs sound + attenuates reflection of high-freq sounds
Hearing:
- Their tympanic ears have only 2 auditory neurons but tuned to bat call freq range (A1 and A2)
- Noctuid moths display two distinct behavioural responses
- > Fly away if call is far (A1)
-> Fly erratically if bat is close (A2)
Production of sound
- Some toxic tigers moths have tymbal that makes v high freq sound confusing the echolocation of the bat -> sonar jamming (acoustic aposematism)
- Other species do Batesian mimicry of toxic tiger moth sounds
Anti- Anti- predator in bats
Some bats have evolved to be quieter
Example: The barbastelle bat
- Calls unusually quietly
- Eats mainly eared motsh
- As no other ecological benefit for calling quietly can concludequiet calling might be a counter-counteradaptation to insect ears
Convergent principles of sensirimotor systems in animals
o tympana to detect pressure waves, and hairs to detect particle motion;
o fast ionotropic transduction mechanisms to transduce sound stimuli;
o morphological computation to simplify neurological computation;
o tonotopic representation of different frequencies of sound;
o parallel processing by neurons acting as matched filters.
Overall
Types of ears:
- atypanic
- Tympanic
Ionotropic transduction and tonotonic representation of frequencies in basillar membrane and tympanic membrane
Mechanisms for localising sound
- Vertical: filtering
- Horizontal: delay
- morpholgical computation in smaller organisms
Echolocation
- neurological mechanism
- Call design
- > Broadband
- > Narrow spectrum
- > Constant frequency
Anti predator mechanisms in moths
- Stealth
- hearing
- Sound production
Anti anti predator mechanisms in bats
- Quieter echo location
