Localization

Question 0

Intensity Differences

Answer 0

sound at ear closer to source is slightly more intense (louder) than at another ear, because of Head Shadow

works best for higher frequencies, since these are most likely to be absorbed by the head

Question 1

Localization

Answer 1

can use:

INTENSITY differences

PHASE differences

or TIMING differences to the two ears

just as in visual system, a disparity between the inputs to two receptors (2 eyes, 2 ears, etc) is used to perceive depth

Question 2

Head Shadow

Answer 2

or acoustic shadow is a region of reduced amplitude of a sound because it is obstructed by the head.

Sound may have to travel through and around the head in order to reach an ear.

Question 3

Phase Differences

Answer 3

for lower frequencies

can detect difference in peak vs. trough of wave reach two ears

Question 4

Peak

Answer 4

oscillating molecules most condensed

Question 5

Trough

Answer 5

oscillating molecules most rarefield - widely spread out

Question 6

Timing Differences

Answer 6

to the two ears via “Interaural Time-Disparity Detectors”

found in monkey Superior Olive (& A1)

e.g. if sound reaches the right ear first, “Onset Cells” in right Cochlear Nucleus fire before those in left Cochlear Nucleus

Question 7

Onset signal race…

Answer 7

…to same Superior Olive nucleus

Signal travels on axon with a branch to each Superior Olive cell in an array

e. g. if right signal arrives long before left, it travels farther along array toward left side when left signal soon enters
- Since input from both right and left Onset cells are required to trigger a response from a Superior Olive cell, only a cell at the left of the array (in the above example) will fire, indicating sound source reached right ear first

Question 8

if sound arrives slightly before the other

Answer 8

… right and left Onset signals will meet closer to the center of the Superior Olive array, etc…..

Question 9

If Onset Signals arrive at Superior Olive at the same time….

Answer 9

….they meet in the center of the array

sound localized equi-distant from 2 ears

from left/right distinction: Sound from ahead/behind disambiguated by other cues = > e.g. Intensity difference

Question 10

in conclusion, these detector cells respond to…

Answer 10

….different ranges and direction of disparity in arrival time to the two ears