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

9/16/2011 Krogh’s Principle Linear Summation Delay ‐ line Coincidence Detector + Σ Σ ‐ L13. Sound Localization Σ delay ∞ September 16, 2011 ∫ τ = + τ ⋅ τ r ( ) f ( t ) h ( ) dt BioNB4240 − ∞ C. D. Hopkins 1 The mobbing calls of different species of birds, given in response to Aerial alarm calls of different species of birds are very similar. a sitting predator (cat, owl). Alarm calls of 5 species of British birds given in response to spotting an overhead hawk. (Marler, 1955) 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. 3 4 Chickadee sees predator sitting in tree. Robin sees a hawk Mobbing calls attract flock members to alert other birds. •slow onset and offset •whistle ‐ like •narrow frequency sharp onset range •not repeated click ‐ like broad Alarm Call (warns baby birds) bandwidth repetitive 5 6 1

9/16/2011 Why are the mobbing calls so similar? Why are the hawk calls similar? Marler’s Hypothesis: Marler’s Hypothesis: “chatter” calls are easily locatable (ideal for calling “Tseet” sounds are difficult to locate (ideal for alerting conspecifics and young to look up attention to where the owl is hiding) and hide). oscillogram of 1. 1. gradual sound onset and offset poor timing gradual sound onset and offset – poor timing 1) Sharp onset and offset � inter ‐ aural timing � i sounds d 1) Sh d ff l i i cue cues. 2. too high freq for phase determination. 2) Repetitive � redundant. 3. too low frequency for sound shadowing. 3) Broad bandwidth ‐ low frequencies provide good phase cue ‐ high frequencies provide good inter ‐ aural amplitude cue (shadow of head) 7 8 Humans have difficulty locating 3 kHz tones. sound localization c λ = f d Steven and Newman, 1934 phase ambiguity 10 when λ < d Auditory Binaural Cues pathways Two cues for Cats: ITD IID = ILD ITD: (varies between 0 and 400 dorsal view microsec) mammalian ILD is strongest at high frequencies brain >5 kHz for cats, >2 for humans d = .136 m ITD = 0.136 m / 340 m/s 12 11 2

9/16/2011 Auditory Pathway Wiring LSO receives inputs from 2 sides • Cortex • Thalamus • Inferior C lli Colliculus l • Lateral lateral superior olive lemniscus • Brainstem medial nuc. trapezoid body 14 13 contralateral intensity LSO responds to ILD 16 15 Auditory Pathway Wiring Cells in MSO act as coincidence detectors • Cortex • Thalamus • MSO neurons fire best when stimulated with a particular ITD. Using sine • Inferior waves, this means one particular phase C lli Colliculus l difference. • MSO units phase lock to monaural and to binaural • Lateral medial superior olive stimulation. • Best IPD corresponds to lemniscus difference in response phases for two ears. MSO is a coincidence detector. • Brainstem 18 17 3

9/16/2011 Cells in MSO act as coincidence Jeffres’ Model (1948) detectors • Suppose Right & Left neural inputs from opposite sides • MSO neurons fire best converge.... when stimulated with a • Delays, from neuronal particular ITD. Using sine waves, this means one conduction particular phase • • Output cells (A ‐ E) fire only if Output cells (A E) fire only if difference. there is coincident inputs from • MSO units phase lock to both R and L monaural and to binaural stimulation. • Delay ‐ Line + coincidence • Best IPD corresponds to detector produces a map of difference in response azimuth. phases for two ears. MSO is a coincidence detector. 19 20 21 Barn Owl Barn Owls Roger Payne • R. Payne (1971) * establishes that barn owls use passive listening to detect and localize prey. • owls turn head toward sound. • leave perch, track sounds. • owl attacks sound, not mouse. • Owls are using passive listening (not echolocation!) * Payne, R. S. (1971) Acoustic location of prey by Barn owls ( Tyto alba ) 24 4

9/16/2011 Ear Asymmetry in Barn Owls Owl can “localize” before leaving perch. Owl attack is precise within 2 degrees. Owl attacks sound source, not the Asymmetry in ear openings direct sound mouse. from above or below. •Conclusion: good localization in both vertical vertical As sound position varies in vertical angle: A d i i i i i l l (elevation) and horizontal (azimuth) ILD in two ears. •How do they localize in the vertical? 25 26 In barn owls, asymmetric ear placement In barn owls, asymmetric ear placement converts IID into map of elevation converts IID into map of elevation y= x 2 y= x 2 1 1 0.8 0.8 0.6 0.6 0 4 0.4 0.4 0 4 Left ear Left ear 0.2 0.2 Right ear Right ear 0 0 -0.2 -0.2 -0.4 -0.4 -0.6 -0.6 -0.8 -0.8 -1 -1 27 28 0 0.5 1 0 0.5 1 to be continued….. 5