lecture 12- sound localisation and sensory interaction Flashcards
what are the main things sound localisation is needed for
survival
perception of auditory space
what are the 2 different ways we can localise sound
detection of interaural level differences in the horizontal plane
detection of interaural timing differences (arrival times)
which way of localising sound is used for high frequency sounds
level differences in horizontal plane
which way of localising sound is used for low frequency sounds
timing differences
where does sound localisation occur (pathway)
cochlear nucleus -> lateral superior olive -> medial superior olive
describe detection of ILDs in general
neurons in LSO receive excitatory input from near ear and inhibitory input from far ear
these summate
describe ILD in left ear when sound is coming from the left
ILD maximal and +ve
louder the sound = more neurons stimulated
describe ILD in left ear when sound is coming from the centre
loudness in each ear is the same
output is half of maximal (inputs are balanced so not 0 )
describe ILD in left ear when sound is coming from right diagonal
ILD increases but becomes -ve for left LSO
inhibitory input becomes larger than excitatory
describe ILD in the left ear when sound is coming from right
ILD is maximal in -ve direction
what does an overlap in LSO output graphs for the left and right ear allow for
rapid detection and accurate sound localisation
describe detection of ITDs in general
neurons in MSO receive 2 excitatory inputs - one from each ear
maximal activity only achieved when both inputs arrive at the same time
neurons are different lengths (eg. for the left MSO the left neuron is shorter than the right one so the right will take longer)
describe detection of ITDs in the left ear when sound is coming from the left
input from left ear arrives first
input from right ear reaches MSO after MAXIMAL delay
describe detection of ITDs in the left ear when sound is coming from left diagonal
slight less delay of right ear as sound is coming from position closer to it
describe detection of ITDs in the left ear when sound is coming from the centre
sound itself reaches the ears at the same time (ITD = 0) BUT
still a delay from right ear due to the longer nerve
population output is half maximal
describe sound detection of ITDs in the left ear when sound is coming from the right diagonal
delay is very small
population output becomes large
describe sound detection of ITDs in the left ear when sound is coming from the right
longer nerve distance of right nerve is overcome by the time delay as sound is at right ear
population output is highest
describe the graph for MSO output for the left ear
increases from L -> R in a convex slope
describe the experiment done with barn owls to test the visual and sound circuit interactions
shifted visual field by 20 degrees to the left, then allowed owls to adapt
measured head orientation and compared to a magnetic field
describe the results of the owl experiment
before prisms= head points directly towards visual and auditory stimulus
after day 1= head still quickly adapts to 20 degree change ( turns 20 degrees to right) and still directly faces sound stimulus
after day 42= same visual shift response
also now have a 20 degree shift in auditory response, even when sound is infront
after prisms removed= visual response realigns, auditory response remains shifted
what is the key finding from the barn owl experiment
the auditory space map is modified based on the changes to visual map
visual map dominates and is used to teach interpretation of auditory cues
