What is an auditory space
-it exists where there is sound
What are two types of location cues
- binaural cues
- > depend on both ears
- monaural cues
- > depend on just one ear
What are the three dimensions in which people can locate sound
1) Azimuth
- >extends from the left to right
- >determined by binaural cues
2) Elevation
- >extends up and down
3) Distance
- >distance of the sound source from the speaker
What are the two binaural cues
1) Interaural level difference
2) Interaural time difference
What is the interaural level difference
- it is the difference of the sound pressure level
- >of the sound reaching the two ears
How does the acoustic shadow describe the intaural level difference
- difference in the level of the sound pressure reaching the ears creates an acoustic shadow
- > it reduces the intensity of sound that reaches the far ear
- > occurs reduction of intensity at the far ear for high frequency sounds
- > not for low frequency sounds
- basically your head fits in between high frequency waves because there is enough distance between the high frequency waves
- > so high frequency waves have an impact on intensity
What cue is the intaural level differnce good for
-it is good for location of high frequency sounds
Describe ITD. How is it effected
-it is the time difference between when a sound reaches the left ear and the right ear
- when a source is located to the side
- > there is a difference in when sounds reach one ear and when they reach another
- ITD becomes larger as sounds sources are located more to the side
- > most effective for determining low frequency sounds
-ITD is the dominant binaural cue for hearing
What is the cone of confusion
- it is when all on points on the surface of the cone have the same ILD and ITD
- there can be large or small cones
- basically, many locations in space where sounds could results in same ILD and ITD
What does monaural cues provide information on
-it provides info on elevation
What is the primary monaural cue for localization
- it is spectral cues
- > works especially for high frequency sounds
- note the differences in the way sounds bounce around within the pinnae
- > create different frequencies for the two locations
- note the nooks and crannies of the pinnae are important for determining elevation
- > without it, it is difficult to locate sounds along the elevation coordinate
What is the Jeffress model of auditory localization? Also describe the coincidence detectors within this model
- it proposes that neurons are wired
- > so they each receive signals from the two ears
- if the sound source is directly in front of the listener
- > sound reaches the left and right ears simultaneously
-coincidence detectors only fire when signals from the left and right ear both reach a neuron at the same time
Relate ITD detectors to the Jeffress model
- ITD detectors each fire to a specific ITD
- this model suggests that each neuron fires to a specific ITD
- it is in a specific area, referred to as a place code
- > place code is where that activity occurs
What is an ITD tuning curve
- it describes the properties of ITD neurons
- > plots the neuron’s firing rate against the ITD
- each neuron in each ear responds to a different ITD
Describe the neuronal coding for sound localization in birds vs mammals
- in birds
- > it is a sharply tuned neuron
- > code for birds is a place code
- > ITD is indicated by firing of nervous systems at a specific place
- in mammals
- > the neurons are broadly tuned
- > code for mammals is a population code
- > ITD is determined by many broadly tuned neurons working together
- > the left hemisphere fires for sounds coming from the right side and vice versa
Where does the neural basis of binaural localization begin
- it begins along the pathway from the cochlea to the brain
- >in the superior olivary nucleus
How has the A1 been shows to have a role in localization
- lesioning A1 in ferrets decreased
- > did not eliminate ferret’s ability to localize sounds
-deactivating A1 in cats results in poor localization
Where is the posterior belt area
-located near the back of the cortex
Where is the anterior belt area located
-it is located toward the front of the cortex
Describe the response of sound localization of the A1 to the posterior belt area
- A1 responds to a larger area of space for sound localization
- > posterior belt area responds to a smaller space
- > therefore, the posterior belt area provides more precise information about the location of sound sources
-note the posterior belt tuning curves are narrower than A1 tuning curves
Describe the role of anterior belt area
- neurons here respond more to complex sounds
- > do not respond as well to pure tones
-so anterior belt areas are more involved in identifying complex sounds
What happens when you deactivate the anterior belt
- you disrupt the ability of the cat to tell the difference between the two timing patterns of sound
- does not affect the cat’s ability to localize sounds
Distinguish posterior area belt and the anterior area belt
- posterior is involved in localizing sounds
- anterior is involved in perceiving complex sounds from one another
Where is the what auditory pathway located and where is the “where” auditory pathway located
- what
- > it is located in the anterior belt and the temporal lobe
- > also frontal cortex
- where
- > it is located in the posterior belt
- > also located in the parietal
- > finally again frontal cortex
