Figure 10.13, page 344

Ear—overall view

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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.

The barn owl (Tyto alba)

amazing performanceon sound localization tasks

azimuth

elevation

leftear

Inter-aural Time Difference(ITD)

Inter-aural Level Difference(ILD)

Inter-aural Level Difference (ILD)

AcousticShadow

Figure 12.5. 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 person’s head, so the sound is unaffected by the head.

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 listener’s right before it reaches the left ear.

Inter-aural Time Difference (ITD)

Inter-aural Time Difference (ITD)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

How the Jeffress circuit operates

The barn owl (Tyto alba)

For owls.....

the horizontal position (azimuth)of a sound source is computedwith interaural time differences(ITD)

-the vertical position (elevation) is computed using interaural sound-level differences (ILD)

Barn Owls do use ITDsto localize sounds in azimuth

Barn Owls do use ILDs

to localize sounds in elevation

How owls use ILDs as a cue for elevation of a sound source.

Barn Owl (Tyto alba)

Jamaican Owl – Pseudoscops grammicus

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

Great Grey Owl – Strix nebulosa

Barn Owls do use ILDs

to localize sounds in elevation

Neural Processing-different pathways compute ITD and ILD, and information converges at ICx (MLd)

NucleusMagnocellularis

(NM)

MLD

NucleusLaminaris

(NL)

NucleusAngularis

(NA)

ITDIID

A

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

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

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

THERE IS A “SPACE MAP” in MLD

Cell in MLD respond to a particular ITD

Are we like the Owls?

Figure 12.12 (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).

Directional transfer function

For humans, the pinnae are important for localizing the elevation of sound sources

– performance after the molds inserted

– adaptation

Auditory Scene Analysis

-direct vs. indirect sound

Precedence Effect

-for sounds arriving within 5 msec, the location is based on the first sound

-it's not the loudnessof the first sound that is

important

-later sounds do have an effect on sound quality

Precedence Effect

Reverberation time

-time it takes for sound to decrease to 1/1000the original pressure

-too short - music sounds dead

-too long - muddled

-optimal is 1.5 to 2 seconds

-direct vs. indirect sound

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.

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.

Vision

Audition

pattern of light perception of objects

vibration of basilarmembrane

perception ofauditory streams

Gestalt Psychology

Similarity

time

Principles of Auditory Grouping

Vision

Audition

pattern of light perception of objects

vibration of basilarmembrane

perception ofauditory streams

Gestalt Psychology

Similarity

time

auditory stream segregation

Figure 11.24, page 398

Grouping into high and low streams

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Stream Segregation in a Series of Six tones (1)

Stream Segregation in a Sonata be Telemann (6)

Figure 12.18 (a) These stimuli were presented to a listener’s left ear (blue) and right ear (red) in Deutsch’s (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).

easyor

difficult

easy

auditory stream segregationRelease of a two –tone target by the capturing of interfering tones (16)

Stream segregation can effect perception of timing (13)

Stream segregation in African xylophone music (7, 8, 9)

Figure 12.19 A demonstration of auditory continuity, using tones.

Demonstrations 28,29, 31

Good Continuation

phonemic restoration effect

The (cough)eel was on the orange.

Percept

peelThe (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