Auditory System 2: Central Pathways Flashcards
Where is the first “binaural” (bilateral auditory) input?
The superior olivary nucleus
Where do axons from the superior auditory nucleus travel?
Up the lateral lemniscus to the medial geniculate body of the thalamus.
How is the azimuth (horizontal angle) of low frequency sound determined?
Interaural time difference.
Where in the superior olivary nucleus is time difference encoded?
The MSO - medial superior olivary nucleus
What’s the mechanism for determining azimuth in the MSO?
Near ear info travels contralaterally, far ear info travels ipsilaterally. A series of neurons corresponding to different angles are present. They only fire when signals from both ears hit them simultaneously. The axon length leading to them varies.
How is the azimuth (horizontal angle) of high frequency sound determined?
Interaural level (intensity) difference.
Where in the superior olivary nucleus is interaural level difference determined?
In the lateral superior olive (LSO). Don’t worry about the mechanism.
How do you determine if a sound is in from of or behind you? How about if it’s above or below you?
Monaural clues - based on how difference simple frequencies bounce off the inner ear.
Do we have to learn the relationship between interaural time/level difference and spatial location? Why does it change?
Yes. It changes as the size of one’s head grows. Or when you get big ear piercings.
What are the 3 levels of processing in auditory cortex?
Core (primary areas), belt, and parabelts
Which levels of processing respond to simple sounds? To complex sounds?
Simple sounds: core areas
Complex sounds: belt and parabelt
What are the 3 primary auditory areas in the core? How do we know?
AI, R, and RT (… probably doesn’t matter)
The thalamus sends info there.
Is frequency information representend in a topographic (tonotopic) fashion in the auditory cortex?
Yeah. Different areas respond to different frequencies.
Where is sensitivity to certain specific types of sounds increased?
In secondary auditory areas (such as Wernicke’s area being more sensitive to speech)
Who has trouble splitting apart what sounds are coming from where?
Old people, people with cochlear implants and hearing aids
