PSYB51H3 Chapter Notes - Chapter 10: Sound Localization

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Published on 12 May 2011
School
UTSC
Department
Psychology
Course
PSYB51H3
Chapter 10: Hearing in the Environment
Sound Localization
Sounds are processed in same place in ear no matter where it comes from
Having 2 ears allows us to tell location
oCloser objects heard at one ear first (timing), intensity greater (louder)
Interaural Time Difference
Interaural time difference (ITD): diff in time btw sound getting to an ears
Azimuth: angle of object relative to imaginary circle around us
oi.e. horizontal plane
Largest ITD is at extreme L/R (90°) w/ delay of 640 microseconds
oAs we move further away from extremes delays are less
Directly to the front and back, there are is no ITD
PHYSIOLOGY OF ITDs
Medial superior olives (MSOs): relay station in brain stem, inputs from ears
combine to detect ITD
ITD detectors form connections in first few months of life
Size of head is important for interpreting ITDs
Interaural Difference
Interaural level difference (ILD): diff in intensity btw sound arriving at one ear
oSimilar properties as ITD
Sounds more intense for closer ear
ILD largest at extreme L/R (90°) , none at front/back
Btw angles not as correlated b/c of head shape
ILD greatest for high freq tones
oBecause low freq bends better
oILD is almost zero below 1000Hz (low freq)
PHYSIOLOGY OF ILDs
Lateral superior olives (LSOs): relay station in brain stem, inputs from ears
combine to detect ILD
LSO is excited/inhibited
oExcited by ipsilateral ear
e.g. excitatory connections from L LSO comes from L cochlea
oInhibited by contralateral ear
Via medial nucleus of trapezoid body (MNTB)
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Sensitivity comes from:
oSound thats more intense in one ear better at exciting LSO of same ear and
inhibiting LSO of other
Cones of Confusion
Cone of confusion: positions where sounds produce same ITD and ILD
oi.e. same ITDs and OLDs
Wallach demonstrated if we think were moving and hear sound in front of us, we
think sound is directly above/below us
oHead is fixed and we think there are only 2 points sounds remain constant
Moving head differentiates btw regions that have same ITD and ILD
oWhen head is moved ITD/ILD changes
oE.g. Fig. 10.8 moving head will make another 2 regions have same ITD/ILD,
but only 1 is consistent before & after head turn
Pinna and Head Cues
Pinnae shape funnels certain frequencies better than others and frequencies vary
depending on direction
Engergy at eardrum for diff freqs isnt constant even if presented so
Intensity of freq changes with elevation as well
Head related transfer function (HRTF): function, describes how pinna, ear
canal, head and torso change intensity of sounds w/ diff freqs at diff locations
oCant be simulated like ITD/ILD because its diff for every person
We adapt to HRTF through experience and reinforce with vision and other sources of
info
Auditory Distance Perception
Use relative intensity to judge distance
oThe further away sound is the less intense it is
oCan make mistakes if sound is same, but just softer
Inverse square law: as distance, intensity faster. intensity = distance²  
Good at using intensity diff to tell distance close, bad when distance is far
oWorks best during movement
Also use spectral composition to tell distance
ob/c air absorbs high freq more than low, further sounds are lower in freq
oonly for more than 1k
also use relative amounts of direct versus reverberant energy to tell distance
oi.e. direct energy is usually from close objects, further object sounds bounce
off surfaces
Complex Sounds
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Document Summary

Sound localization: sounds are processed in same place in ear no matter where it comes from, having 2 ears allows us to tell location, closer objects heard at one ear first (timing), intensity greater (louder) Interaural time difference (itd): diff in time btw sound getting to an ears: azimuth: angle of object relative to imaginary circle around us, i. e. horizontal plane. Largest itd is at extreme l/r (90 ) w/ delay of 640 microseconds: as we move further away from extremes delays are less, directly to the front and back, there are is no itd. Physiology of i t ds: medial superior olives (msos): relay station in brain stem, inputs from ears combine to detect itd. Itd detectors form connections in first few months of life: size of head is important for interpreting itds. Interaural level difference (ild): diff in intensity btw sound arriving at one ear: similar properties as itd.