Audition Flashcards
Variance across Species
based on different needs
land/water/air, long distances, high/low frequency sounds, etc
External Impact
evolutionary structures of the auditory systems
Basilar Membrane and Species
contains hearing receptors - sounds of different frequencies are processed along different areas of the membrane
- cares in length across species
- shorter in amphibians and reptiles, longer in birds, longest in mammals
- longer membrane allows processing of a wider range of frequencies
Sound Waves
The Stimulus
Alternating bands of more and less condensed air particles interact with the eardrum to begin auditory processing (compressed air pushes eardrum inward; less dense cause s eardrum movement outwards)
-travel much slower than light waves and require some medium to travel through
-causes the air molecules surrounding the source to move, causing a chain reaction of moving air particles
Sound Initiation
vibrating object
burst of air
forcing air through a small cavity
3 Psychological sound waves
Loudness
Pitch
Timbre
Amplitude
measure of loudness
- greater amplitude = greater intensity/higher waves = louder sound
- measured in decibles
- too loud can cause damage
- 60 decibles = normal convo
Frequency
measure of pitch (distance between peaks)
- measured in Hertz (Hz) - number of cycles per second/number of times a second that a cycle is made
- many peaks = high frequency
- audible zone of frequencies that humans can detect represent only a portion of the possible frequencies that can be produced
Timbre
measure of complexity/purity
-most of the sounds that we hear everyday are complex sound that are composed of multiple sound waves that vary in frequency
The Ear
detects the sound waves and convert them into something that the brain can understand
3 Layers of the Ear
External, Middle, Inner
- each area conducts sound in a slightly different way
- incoming changes in pressure are channeled though the external onto the middle, and amplified so it can be detected as changes in fluid pressure, converted into auditory neural impulses
External Ear
Pinna
Canal
Eardrum
Pinna
folded cone that collected sound waves in environmental and directs along the ear canal
Canal
narrows toward ear drum, amplifies incoming sound waves
Eardrum
thin membrane vibrating at the frequency of the incoming sound wave and forms back wall of ear canal
Middle Ear
other side of eardrum
Ossicles
Ossicles
3 Bones called hammer, anvil, stirrup
- create a lever system to amplify vibrations
- convert to waves in the fluid filled inner ear
- 20 times larger than oval window to which it is connected
Inner Ear
Coclea Oval Window Round Window Basilar Membrane Hair Cells
Cochlea
fluid field tube about 35mm long
- coiled like a snail shell
- contains neural tissue necessary to transfer changed in fluid to neural impulses of audition
Oval Window
small opening in side of cochlea
-when vibrates, causes displacement of fluid in cochlea
Round Window
located at other end of cochlea
-accommodates for movements of fluid by bulging in and out accordingly
Basilar Membrane
flexible membrane inside cochlea
- when pushed downwards, fluid inside cochlea causes round window to bulge out
- when pushed upwards, round window bulges inwards
- gets wider towards the end
- varies in flexibility and width, so sounds of different frequency cause different areas to vibrate
- higher frequency = near oval window; low frequency = near round window
Hair Cells
auditory receptors in Basilar membrane
- move when membrane moves in response to waves in fluid
- movement is converted into neural impulses
- release neurotransmitters when activated and from synapses with bipolar cells, whose axons make up the cochlear nerve
- outnumbered 4:1 but mainly contribute to signal
Cochlear Nerve
outer hair cells are more numerous. but slower
- inner hair cells are less numerous but faster and have more connections
- axons synapsed with outer are unmyelinated and thin; axon synapsed with inner are myelinated
Cochlear Nucleus
located in hindbrain
- has separate dorsal and ventral streams
- receives signal from EPSPs in cochlear nerve fibres which are triggered by neurotransmitter released by hair cells
Topographical Organization
hair cells connect to the cochlear nerve such that neighbouring regions of hair cells remain together - maintained throughout auditory cortex
-different frequencies at different points on basilar membrane - info about similar frequencies are processed together
Auditory Localization
ability to locate a source in space based on the fact that our sense organs are separated in space
- there is no spatial may for audition - calculated from neural representations of incoming sound
- the fact that our ears are located on opposite sides of our head in interaural differences in the sound that give cues for auditory localization
- sound must travel farther to reach on ear as opposed to the other which gives cues to localization
Time-Difference
measured in sub-milliseconds
- dependent on direction of incoming sound
- specific neurons in superior olivary complex to thinking of arrival of action potentials
Interval Difference
loss of intensity for farther ear
- close sounds - detectable
- farther sounds - rely in difference in intensity caused by the head which casts a sound shadow
- diminished intensity at distal ear
- differences can be calculated and compared to determine location
Sounds In front/behind
have little difference
- harder to locate source
- head rotation is a solution
Pinna Cues
defracts incoming sound waves to make changes to frequency content
- changes
- used for localization
- ear print =- every ear is different
- alteration causes disorienting effect
Echolocation
process by which a receiver emits sound pulses and analyzes the returning echo to form a perceptual image of objects in the environment
- high frequencies bounce off objects and return to the bats ears
- outgoing sound waves
- analyzes slight differences in frequency content and timing of returning sound waves to determine characteristics
- proximity
- still versus motion (doplar)
- texture
Co-Evolution
the process by which the evolution and adaptation of traits of one species can directly affect the evolution of traits in another species
-prey learning to detect bat calls (increases moth survival rate by 40%)
Paul Farvue
selective pressures of a predator can drive evolution of a defensive trait of a prey (can result in further selection pressures on predator and so on)
-interact individually; locked in arms race
