Binaural hearing. Prof. Dan Tollin on the Hearing Throne, Oldenburg Hearing Garden

Transcription

1 Binaural hearing Prof. Dan Tollin on the Hearing Throne, Oldenburg Hearing Garden

2 Outline of the lecture Cues for sound localization Duplex theory Spectral cues do demo Behavioral demonstrations of pinna cues SOC circuits for encoding ITD/ILDs How do we show that the role of the SOC is to encode binaural localization cues? Behavior Effects of lesions on behavior Or even better, effects of stimulation on behavior Anatomical evidence Response properties of neurons: how do they respond to manipulations of that parameter? ITDs: characteristic delay

3 Visual vs auditory localization Visual world is mapped onto the retina. Visual localization requires preserving anatomical retinotopy. Spatial information is not represented in the cochlea. Auditory system has to compute space

4 What are the acoustic cues for localization? Binaural cues for horizontal localization Interaural time differences (ITDs) Interaural level differences (ILDs) Spectral cues for vertical localization Counter-intuitively, the spectrum of the sound helps us to localize it in the vertical dimension

5 Duplex theory of sound localization Low frequencies Requires phase locking (< 3 khz) Very high resolution (jnd = 5-10 sec) High frequencies Short (reflects from head, ears)

6 Effect of wavelength and size of object constant, size varies Size constant, varies

7 Head-related transfer functions (HRTFs)

8 Spectral cues are important for vertical localization

9 Demo of pinna cues

10 Pinna cues can be distorted chronically in human subjects Hofman et al., 1998

11 Distorted HRTFs affect vertical sound localization Human subjects can adapt to distorted HRTFs Curiously, there is no aftereffect Hofman et al., 1998

12 Pinna movements aid bats in wire avoidance during flight Mogdans et al., 1988

13 How do we encode these pinna cues? The type IV cells in the DCN have properties that suggest sensitivity to the notches in pinna cues. Lesions of DCN also suggest a role of DCN in localization in elevation.

14 Reiss and Young, 2005 Type IV responses to notched noise

15 Young et al., 1992 Type IV units are sensitive to notch noise stimuli, like HRTFs

16 Type IV cells show strong inhibition with a notch at CF

17 Effects of DAS lesion on head orientation Control DAS lesion May, 2000

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20 Virtual acoustic space In addition to providing information on source elevation, the HRTFs of the sound also externalize the sound when heard over headphones. Since the HRTF measurements are not from your own ears, these effects vary considerably from subject to subject.

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23 Saccade task

24 Adapted from Geisler, 1998, courtesy W. Welker What do the ears do?

25 Pinna movements during localization

26 With the head restrained, cats undershoot acoustic targets Populin and Yin, 1998

27 Pinna movements to visual and acoustic targets Populin and Yin, 1998

28 Pinna movements are largely on the ipsilateral side Populin and Yin, 1998

29 Pinna movements have very short latencies

30 Auditory localization improves markedly with the head unrestrained

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32 With the head free, cats localize sounds about as well as barn owls and people

33 What are the ears doing? Vestibulo-auricular reflex (VAR): The left pinna moves reflexly to compensate for a leftward head movement VAR

34 The vestibular-auricular reflex (VAR)

35 Frens and van Opstal, 1995 Localization in elevation requires wide band spectral sounds

36 Cat 28 A 40 Noise 500 Hz 1000 Hz 2500 Hz 6000 Hz 20 0 o o o o o -20 Elevation (deg) B Target Response Target Response B Azimuth (deg) Gaze Shift Elevation (deg) = 4.42 Gain =.86 n = 549 = 7.73 Gain = 0.01 n = 257 = 7.94 Gain =.11 n = 340 = 7.74 Gain =.07 n = 315 = 7.13 Gain =.07 n = Gaze Shift Azimuth (deg) = 4.14 Gain =.78 n = 549 = Gain =.85 n = 257 = Gain = 1.00 n = 340 = Gain =.85 n = 315 = Gain =.69 n = Motor Error (deg)

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38 Binaural beats (or rotating tones) f f + f b

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40 Characteristic delay Rose, Gross, Geisler and Hind, 1966 Jerzy Rose

41 Shig Kuwada, U Conn Kuwada and Yin, 1983

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43 Yin and Kuwada, 1983

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46 Other important or interesting binaural phenomena Binaural masking level differences Huggins pitch

47 Binaural masking level differences (BMLDs)