Auditory
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What is sound?
• a compression wave generate by vibrating air molecules
What can complex sounds be represented as?
• the sum of multiple simple sine waves
What does the amplitude of the sound correspond to?
• intensity
What does the speed of the sound depend on?
• the conduction medium
We and other animals are ____ to some frequencies than others.
more sensitive
What are the lower and upper limits of frequency sensitivity called?
• lower limit: threshold - upper limit: perception limit
We can hear sounds within the range of frequencies of what?
• 20 - 20K Hz
Small mammals are sensitive to ____ frequencies.
higher
What do animal auditory systems emphasize detection of?
• frequencies that are in their vocalizations
What kind of frequencies do echolocating animals rely on?
• very high frequency vocalizations to resolve spatial features of target
What specifications in frequency range do animals that have to avoid predators have?
• often emphasize the low frequencies that conduct through the ground from movements of approaching predators
What are the different parts of the middle ear?
• malleus • incus • stapes • tympanic membrane • oval window
What do the external and middle parts of the ear do?
• collect sound waves and amplify their pressure to transfer that energy to the fluid filled cochlea of the inner ear
What are the parts of the external ear?
• pinna (upper lobe) • concha (cartilage rings) • auditory meatus (tunnel)
How does the external ear amplify and focus energy?
• does so selectively for frequencies around 3 kHz by passive resonance effects
What is the other function of the outer ear?
• contributes to localization of sound in space - specifically elevation of sound source
Why is it a problem that the sensory “detectors” are immersed in fluid?
• the sound signal is due to moving air - fluid is much heavier than air
What is the tympanic membrane?
• “ear drum” - large relative to the base of the stapes where contact is made (concentrating large area)
What are the ossicles?
• inner ear bones - malleus, incus, stapes
What function does the lever action of the ossicles provide?
• provides mechanical advantage to increase pressure on stapes
What are the muscles called that regulate efficiency of transmission of sound to the inner ear and how do they function?
• tensor tympani and stapedius - control the tension on the bone joints by a reflex response to loud sounds
Why do crickets have central circuits that gate out input from their singing?
• because they don’t have a peripheral system to attentuate loud sounds and they do not block their own song
Which sounds is a 60 yr old particularly insensitive to?
• average loss of 35 dB from 500 Hz to 4 kHz - birds chirping, whspering, alarm clock, leaves rustling, tap dripping
What is presbycusis or presbyascusis?
• high frequency hearing loss with age