L13. Sound Localization delay September 16, 2011 = + - - PDF document

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• L13. Sound Localization

September 16, 2011 BioNB4240

• C. D. Hopkins

Krogh’s Principle Linear Summation Delay‐line Coincidence Detector Σ + Σ

delay

Σ ‐

∫

∞ ∞ −

⋅ + = dt h t f r ) ( ) ( ) ( τ τ τ The mobbing calls of different species of birds, given in response to a sitting predator (cat, owl).

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Sound spectrograms of mobbing calls from 5 species of British birds (Marler, 1955)

Marler, P. (1955). The characteristics of certain animal calls. Nature 176, 6‐7.

Aerial alarm calls of different species of birds are very similar.

Alarm calls of 5 species of British birds given in response to spotting an overhead hawk.

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(Marler, 1955)

Chickadee sees predator sitting in tree. Mobbing calls attract flock members to alert other birds.

sharp onset click‐like broad bandwidth

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repetitive

• slow onset and offset
• whistle‐like
• narrow frequency

range

• not repeated

Robin sees a hawk Alarm Call (warns baby birds)

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Why are the mobbing calls so similar?

Marler’s Hypothesis: “chatter” calls are easily locatable (ideal for calling attention to where the owl is hiding) 1) Sh d ff i l i i

• scillogram of

d

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1) Sharp onset and offset inter‐aural timing cues. 2) Repetitive redundant. 3) Broad bandwidth

‐ low frequencies provide good phase cue ‐ high frequencies provide good inter‐aural amplitude cue (shadow of head)

sounds

Why are the hawk calls similar?

Marler’s Hypothesis: “Tseet” sounds are difficult to locate (ideal for alerting conspecifics and young to look up and hide). 1. gradual sound onset and offset – poor timing

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1. gradual sound onset and offset poor timing cue 2. too high freq for phase determination. 3. too low frequency for sound shadowing.

sound localization

Humans have difficulty locating 3 kHz tones.

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Steven and Newman, 1934 phase ambiguity when λ < d d

f c = λ

Binaural Cues

Two cues for Cats: ITD IID = ILD

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ITD: (varies between 0 and 400 microsec) ILD is strongest at high frequencies >5 kHz for cats, >2 for humans

d = .136 m ITD = 0.136 m / 340 m/s

Auditory pathways

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dorsal view mammalian brain

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Auditory Pathway Wiring

• Cortex
• Thalamus
• Inferior

C lli l

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Colliculus

• Lateral

lemniscus

• Brainstem

lateral superior olive

LSO receives inputs from 2 sides

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medial nuc. trapezoid body

LSO responds to ILD

contralateral intensity

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Auditory Pathway Wiring

• Cortex
• Thalamus
• Inferior

C lli l

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Colliculus

• Lateral

lemniscus

• Brainstem

medial superior olive

Cells in MSO act as coincidence detectors

• MSO neurons fire best

when stimulated with a particular ITD. Using sine waves, this means one particular phase

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difference.

• MSO units phase lock to

monaural and to binaural stimulation.

• Best IPD corresponds to

difference in response phases for two ears. MSO is a coincidence detector.

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Cells in MSO act as coincidence detectors

• MSO neurons fire best

when stimulated with a particular ITD. Using sine waves, this means one particular phase

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difference.

• MSO units phase lock to

monaural and to binaural stimulation.

• Best IPD corresponds to

difference in response phases for two ears. MSO is a coincidence detector.

Jeffres’ Model (1948)

• Suppose Right & Left neural

inputs from opposite sides converge....

• Delays, from neuronal

conduction

• Output cells (A E) fire only if

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• Output cells (A‐E) fire only if

there is coincident inputs from both R and L

• Delay‐Line + coincidence

detector produces a map of azimuth.

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Barn Owl Barn Owls

• R. Payne (1971)* establishes

that barn owls use passive listening to detect and localize prey.

Roger Payne

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• wls turn head toward sound.
• leave perch, track sounds.
• wl attacks sound, not mouse.
• Owls are using passive listening

(not echolocation!)

* Payne, R. S. (1971) Acoustic location of prey by Barn owls (Tyto alba)

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Owl can “localize” before leaving perch. Owl attack is precise within 2 degrees. Owl attacks sound source, not the mouse.

• Conclusion: good localization in both

vertical

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vertical (elevation) and horizontal (azimuth)

• How do they localize in the vertical?

Ear Asymmetry in Barn Owls

Asymmetry in ear openings direct sound from above or below. A d i i i i i l l

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As sound position varies in vertical angle: ILD in two ears.

In barn owls, asymmetric ear placement converts IID into map of elevation

y= x2

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Right ear Left ear

• 1
• 0.8
• 0.6
• 0.4
• 0.2

In barn owls, asymmetric ear placement converts IID into map of elevation

y= x2

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Right ear Left ear

• 1
• 0.8
• 0.6
• 0.4
• 0.2

to be continued…..