audition

Question 1

sound wave vs acoustic energy vs sound

Answer 1

sound wave = physical disturbance caused by the movement of energy travelling through a medium
acoustic energy = produced when a sounds waves makes something vibrate, like a drum
sound = definition depends on your perspective, e.g. monist, naive realist

Question 2

ossicles

Answer 2

malleus → incus → stapes
MIS

Question 3

acoustic reflex

Answer 3

• involuntary contraction of muscles attached to stapes and malleus when intense sound stimuli (70-100dB)
• reduces movement = reduces amplification

Question 4

bending of hair cells

Answer 4

vibration along basilar membrane, causes bending and hair cells against tectorial membrane bend too

• deformation = depolarisation and transmitter release
• onto spiral ganglion cells → axons form auditory part of cochlear nerve

Question 5

innervation of hair cells

Answer 5

• Inner hair cells synapse with afferent fibres of CNVIII (to brain)
• Outer hair cells receive input from efferent fibres of CNVIII (from brain)a

Question 6

amplification of quiet sounds

Answer 6

• for quiet stimuli (<50dB), brain sends signals via CNVIII to outer hair cells, makes them contract
• pulls basilar and tectorial membranes closer together = amplifies vibration
• also bends inner cells → depolarise → more likely to fire

Question 7

coding schemes for auditory info

Answer 7

Tonotopic map maintained from basilar membrane = a place code

And fibres of the auditory nerve will fire increasingly in response to increasing SPL (sound pressure level (dB)) = a rate code

Question 8

projections

Answer 8

• superior olive [medulla]
• inf colliculus ⇒ startle reflex, projections descend to spinal cord
• medial gen nucleus ⇒ final relay station, for processing WHAT and WHERE info
• auditory cortex

Question 9

sound localisation

Answer 9

Interaural time difference
- MSO cells require coincident input to depolarise
- sound reaches L ear before R ear, so coincident firing on MSO cell furthest from L ear and closest to R ear
- not on other cells, bc takes longer for sound to get to R ear and along pathway

Interaural level difference
– head masks sound coming from one side (acoustic shadow)
- if sound primarily coming into one ear, LSO receives excitatory ipsi input and inhibitory contra. input
- = sound localisation
- used to convey WHERE info upstream

Question 10

auditory cortex - progression

Answer 10

Info goes CORE → BELT → PARABELT
- 1º = A1 ⇒ specific frequencies & simple tones (lower order)
- ordered low → high frequency (ant → post)
- 2º = The belt ⇒ respond to complex sounds, sort features of sound (higher order)
- 3º = Parabelt ⇒ a/a

Question 11

dorsal vs ventral stream info

Answer 11

Dorsal stream = WHERE (binaural integration, audiovisual integration - localisation)

Ventral stream = WHAT (sorting sound based on patterns, content, duration and location - identification)

Question 12

Signal-to-noise optimisation

Answer 12

• ventral belts
• masking when amplitude of noise > signal, or when noise and signal similar frequencies (e.g. speech in crowded room)
• to optimise signal:noise ratio
  
  • head shadow effect (turn head, one ear facing signal, tune in to this one)
• attention
• lip reading

Question 13

cocktail party phenomenon

Answer 13

• multi-sensory modality: visual input - read lips
• attention: the concentration of awareness on some phenomenon to the exclusion of other stimuli
• PFC (using ACh) → other brain regions, defining where focus is, top-down processing
  
  • Also to respond to sudden external stimuli → bottom up