BIEB 166 Lecture 18 (WI13)

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Biol/Ecology, Behavior, & Evol
BIEB 166
James Nieh

Lecture 18 Introduction - Sound reception is the reverse of sound generation: a receiver must couple the signal in the medium to itself, modify the signal as needed, and then characterize the signal ○ Take a sound from outside environment, a lower pressure ○ Overcome impedance matching problems ○ Cause vibration in the sound receiving structure Owl - Giant ear face - Funnel sound to go into the holes, ear drums right below the eyes Methods for capturing sounds—coupling Particle detectors - Small levered hairs are deflected when hit by air particles of the near field of a sound - Limited to detecting lower frequencies and slow temporal changes in sound - Widely used by arthropods 1. Inherent directionality - We are able to feel the breeze coming from a specific direction - Sound pressure does not have a inherent directionality - Specific adaptation for animals to know where does the sound come from - Tell inherently where the sound come from (by hair) 2. Do not provide information about sound intensity - All or nothing response - Neurons connecting to the hair structure - Hair moving away from where the particle came Fly antennal aristae - Long hair - Allow animal to hear sound - In fruit flies, the males move their wings to generate particle velocity sound that the female detected ○ Characteristic courtship song ○ Amplitude modulated specifically for different species Parasitoid wasp - Insects carefully eaten the inside structure of the leaf, leaving the outer structure of the leaf - Female is to find the leaf miner and quickly inject the eggs inside - Detects vibrations of leaf miner host ○ Antenna to detect particle velocity sound ○ Cause the air molecules to flick off the leaf - Detect surface vibrations 3. Mechano-sensitive sensilla - Mechano-sensory hairs - Structure is rather large and extremely sensitive to the near-field sound Mosquito Johnston’s organ - Very sensitive! (Eiffel Tower comparison) - Male mosquito, finds the females by the sound they produce 1. Johnston's organ - Almost looks like an antenna - Detect near-field sound being produced by a female - Surrounded by other hairs - Capture any particle of the near-field sound of the particle velocity component - Detect a deflection as small as 0.0001 degrees - Female also has Johnston's organ, but not as developed as the male's 4. Benefits of a particle velocity “ear” - Noise reduction ○ Ignore all the other noise - Sound pressure can carry much longer distance than particle velocity - Only hear things very close by to us - Precise localization ○ Indicates position of waggle dancer Single Pressure detectors Pressure differential detectors Closed cavity covered on at least one side by thin Sample sound field at two locations simultaneously membrane -Differences in pressures causes the membrane to bend one way or the other Detects movement of pressure from one direction Automatically comparing frequencies from two (sample sound at only one location) sides Non-directional Directional -The only way to tell where the sound is -Whichever the pressure is the loudest, that coming from is to move the head to see where would cause the membrane to deflect more the sound is louder -Cannot compare -Samples sound at only one location (where the membrane is located) -Need at least 2 ears to detect direction Respond to near and far fields, but best in far fields Work better in near-fields -Have intrinsic directionality but (like particle detectors) this may be confounded with intensity effects If the membrane is thin, can have wide dynamic Requires two sampling openings far enough apart range and wide frequency response to guarantee differences. Thus limited to higher -Respond to high and low frequency frequencies Moths, cicada, katydid Used in frogs, some birds, and many insects, locust, cricket Ear on each side, relatively thick wall separating the Sound from one ear can alter the information of ears sound coming from another ear -Membrane can bend and deflect Ears as wide apart as possible, easier to detect Ears in legs difference between sound coming in Thin wall separating the detectors -Place ears in legs: separate wide apart Cricket female has to know where the male is Complicated structures to allow sound to come in -Doesn't want to spend long time to find out Very thick wall separating the two pressure the male detectors Ear drum - Cause vibrations of the internal fluid inside the cochlea ○ Eardrum oscillates with changes in pressure - Tympanal organs - Ultimately causing the membrane to vibrate up and down ○ Movement causes neurons to fire - Deflecting hair cells 2 pressure detector ears - Think wall: prevent sound from propagate from one side to another - Pressure wave from left to the right - Left ear: loud pressure Right ear: lower pressure - Brain compare input and determine which way the sound is coming from - Brain compare input and determine which way the sound is coming from Pressure = far-field sound Particle velocity = near-field sound Modification (impedance matching) - This is largely a process of imposing an optimal acoustic impedance between the medium and the organism In a
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