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Figure 10.13, page 344 Earoverall view Copyright © 2002 Wadsworth Group. Wadsworth is an imprint of the Wadsworth Group, a division of Thomson Learning.

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Presentation on theme: "Figure 10.13, page 344 Earoverall view Copyright © 2002 Wadsworth Group. Wadsworth is an imprint of the Wadsworth Group, a division of Thomson Learning."— Presentation transcript:

1 Figure 10.13, page 344 Earoverall view Copyright © 2002 Wadsworth Group. Wadsworth is an imprint of the Wadsworth Group, a division of Thomson Learning Redrawn by permission from Human Information Processing, by P. H. Lindsay and D. A. Norman, 2nd ed. 1977, pg 229. Copyright ©1977 by Academic Press Inc.

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3 The barn owl (Tyto alba) amazing performance on sound localization tasks

4 azimuth elevation

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8 left ear Inter-aural Time Difference (ITD) Inter-aural Level Difference (ILD)

9 Inter-aural Level Difference (ILD) Acoustic Shadow

10 Figure Why interaural level difference (ILD) occurs for high frequencies but not for low frequencies. (a) When water ripples are small compared to an object, such as this boat, they are stopped by the object. (b) The spaces between high-frequency sound waves is small compared to the head. The head interferes with the sound waves, creating an acoustic shadow on the other side of the head. (c) The same ripples are large compared to the single cattail, so they are unaffected by it. (d) The spacing between low-frequency sound waves is large compared to the persons head, so the sound is unaffected by the head.

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13 Figure 12.4 The principle behind interaural time difference (ITD). The tone directly in front of the listener, at A, reaches the left and the right ears at the same time. However, when the tone is off to the side, at B, it reaches the listeners right before it reaches the left ear. Inter-aural Time Difference (ITD)

14 eagle at 10 degrees azimuth x - y =.02m speed of sound = 331 m/s x - y = 60 microseconds i.e. ITD = 60 microseconds x y 20 cm

15 How the Jeffress circuit operates

16 The barn owl (Tyto alba) For owls..... the horizontal position (azimuth) of a sound source is computed with interaural time differences (ITD) -the vertical position (elevation) is computed using interaural sound-level differences (ILD)

17 Barn Owls do use ITDs to localize sounds in azimuth

18 Barn Owls do use ILDs to localize sounds in elevation

19 How owls use ILDs as a cue for elevation of a sound source. Barn Owl (Tyto alba)

20 Jamaican Owl – Pseudoscops grammicus

21 Boreal Owl – Aegolius funerues (Saw Whet Owl, (Aegolius acadicus))

22 Great Grey Owl – Strix nebulosa

23 Barn Owls do use ILDs to localize sounds in elevation

24 Neural Processing -different pathways compute ITD and ILD, and information converges at ICx (MLd) Nucleus Magnocellularis (NM ) MLD Nucleus Laminaris (NL ) Nucleus Angularis (NA ) ITD IID

25 A B Cell A responds to a sound arriving at the left ear before the right ear - an interaural time difference

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27 cells in the dorsal lateral Mesenscephalic nucleus (MLD) are space-specific

28 cells in the dorsal lateral Mesenscephalic nucleus (MLD) are space-specific

29 THERE IS A SPACE MAP in MLD

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31 Cell in MLD respond to a particular ITD

32 Are we like the Owls?

33 Figure (a) ITD tuning curves for broadly-tuned neurons. The left curve represents the tuning of neurons in the right hemisphere; the right curve is the tuning of neurons in the left hemisphere; (b) Patterns of response of the broadly tuned curves for stimuli coming from the left, in front, and the right. Neurons such as this have been recorded from the gerbil (Adapted from McAlpine, 2005).

34 Directional transfer function For humans, the pinnae are important for localizing the elevation of sound sources

35 –performance after the molds inserted –adaptation

36 Auditory Scene Analysis

37 -direct vs. indirect sound Precedence Effect -for sounds arriving within 5 msec, the location is based on the first sound -it's not the loudness of the first sound that is important -later sounds do have an effect on sound quality

38 Precedence Effect

39 Reverberation time -time it takes for sound to decrease to 1/1000 the original pressure -too short - music sounds dead -too long - muddled -optimal is 1.5 to 2 seconds -direct vs. indirect sound

40 Factors that Affect Perception in Concert Halls –Intimacy time - time between when sound leaves its source and when the first reflection arrives Best time is around 20 ms. –Bass ratio - ratio of low to middle frequencies reflected from surfaces High bass ratios are best. –Spaciousness factor - fraction of all the sound received by listener that is indirect High spaciousness factors are best.

41 Acoustics in Classrooms Ideal reverberation time in classrooms is –.4 to.6 second for small classrooms. –1.0 to 1.5 seconds for auditoriums. –These maximize ability to hear voices. –Most classrooms have times of one second or more. Background noise is also problematic. –Signal to noise ratio should be +10 to +15 dB or more.

42 Vision Audition pattern of light perception of objects vibration of basilar membrane perception of auditory streams Gestalt Psychology Similarity time Principles of Auditory Grouping

43 Vision Audition pattern of light perception of objects vibration of basilar membrane perception of auditory streams Gestalt Psychology Similarity time auditory stream segregation

44 Figure 11.24, page 398 Grouping into high and low streams Copyright © 2002 Wadsworth Group. Wadsworth is an imprint of the Wadsworth Group, a division of Thomson Learning

45 Stream Segregation in a Series of Six tones (1) Stream Segregation in a Sonata be Telemann (6)

46 Figure (a) These stimuli were presented to a listeners left ear (blue) and right ear (red) in Deutschs (1975) scale illusion experiment. Notice how the notes presented to each ear jump up and down. (b) What the listener hears. Although the notes in each ear jump up and down, the listener perceived a smooth sequence of notes. This effect is called the scale illusion, or melodic channeling. (Adapted from Deutch, 1975).

47 easy or difficult easy auditory stream segregation Release of a two –tone target by the capturing of interfering tones (16)

48 Stream segregation can effect perception of timing (13) Stream segregation in African xylophone music (7, 8, 9)

49 Figure A demonstration of auditory continuity, using tones. Demonstrations 28,29, 31

50 Good Continuation phonemic restoration effect The (cough)eel was on the orange. Percept peel The (cough)eel was on the orange. The (cough)eel was on the car. wheel The (silence)eel was on the car. eel Phonemic restoration effect

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