Sensation & Perception : Hearing

True, 0.9 degrees difference can be detected

T/F : Humans are very good at sound localization.

Auditory Space

Surrounds an observer and exists wherever there is sound.

Azimuth Coordinates, Elevation Coordinates, Distance Coordinates

What do researchers use to study how sounds are localized in space?

Azimuth Coordinates

Position left to right

Elevation Coordinates

Position up and down

Distance Coordinates

Position from observer

Time, Intensity, Phase Difference, Pinna, Visual Object

What are the direction cues?

Time

Sound must travel different distances to reach the two ears.

• At 90 degrees Azimuth : 0.6 msec earlier than the hidden ear

  • Discriminate up to 10 micro sec.

Binaural Cues

Location cues based on the comparison of the signals received by the left and right ears.

Interaural Time Difference (ITD)

Difference between the times sounds reach the two ears.

False, when distance is the same

T/F : When distance to each ear is different, there are no differences in time.

Intensity

One ear receives the sound directly from the source, and the other ear is in the “sound shadow” or “acoustic shadow” → Intensity Difference

Low Frequency

Bend around the head readily.

• Less than 3000 Hz

High Frequency

Tend to rush right past the hidden ear.

• Exaggerates the intensity difference

Phase Difference

Sound is arriving at two ears in a different portion of its cycle of compression and rarefaction.

• Works better with low frequency sounds

• 1000 Hz : 1 msec → 1 cycle

  • 0.5 msec earlier (62 degrees) → ½ cycle ahead

    • For this, 2000 Hz → Same Phase

Dual Theory of Sound Localization

Low Frequency : Cued by phase difference

High Frequency : Cued by intensity difference

Most Errors Occurred : 2000 - 4000 Hz

Pinna

For vertical, horizontal, front, & back location

• Monaural Cue

True

T/F : Pinna with asymmetrical shape and folds delay or amplify different frequencies by different amounts.

Directional Transfer Function (DTF)

Sounds with different elevation of location gives different levels of intensity with different frequencies.

Visual Object

Interaction between hearing & vision.

• Ventriloquist Effect

Ventriloquist Effect

An observer perceives the sound as coming from the visual location rather than the source for the sound.

Sekuler et al. Experiment

Balls moving without sound appeared to move past each other.

• Balls with an added “click” appeared to collide.

Jeffress ITD Neuron Model

These neurons receive signals from both ears.

• Coincidence detectors fire only when signals arrive from both ears simultaneously.

  • Other neurons in the circuit fire to locations corresponding to other ITDs.

Broadly-Tuned ITD Neurons

Research on gerbils indicates that neurons in the left hemisphere respond best to sound from the right, and vice versa.

• Location of sound is indicated by the ration of responding for two types of neurons.

• This is a distributed coding system.

Hearing Inside Rooms

When a listener is outside, most sound is direct.

• However inside building, there is direct & indirect sound.

Direct Sound

Sound that reaches the listener’s ears straight from the source.

Indirect Sound

Sound that is reflected off of environmental surfaces and then to the listener.

Precedence Effect

Sound may bounce around the room, reflecting from various places, but we don’t experience overwhelming confusion.

• We respond only to the first of the many sounds.

Litovsky et al. Experiment

Listeners sat between two speakers : Lead & Lag Speaker

• When sound comes from lead speaker followed by lag speaker with long delay → Listeners hear two sounds.

• When delay is decreased to 5-20 msec, listeners hear the sound as only coming from the lead speaker → Precedence Effect.

Relative Intensity, Reverberation, Frequency, Loudness Constancy

What are the Distance Cues?

Relative Intensity

Nearer sounds being more intense.

• Familiar sound

Reverberation

Sound reached our ears both directly and after being reflected or reverberated.

False, as the source gets further away

T/F : As the source gets closer, the ratios of direct & indirect sounds are different.

Frequency

Sounds with mostly high frequencies : seem to come from quite nearby.

• High : Easily blocked by obstacles

• Low : Farther away

Loudness Constancy

As speaker moves further, perceived loudness of a sound source remains constant.

Architectural Acoustics

Study of how sounds are reflected in rooms.

Reverberation Time, Intimacy Time, Bass Ratio, Spaciousness Factor

Factors that affects perception in concert halls?

Reverberation Time

Time it takes sound to decrease by 1/1000th of its original pressure.

“Muddled”

If reverberation time is too long, sounds are ______.

“Dead”

If reverberation time is too short, sounds are ______.

2

Ideal times are around _____ seconds.

Intimacy Time

Time between when sound leaves its source and when the first reflection arrives.

20 ms

Best time is around _____.

Bass Ratio

Ratio of low to middle frequencies reflected from surfaces.

True

T/F : High bass ratios are best.

Spaciousness Factor

Fraction of all the sound received by listener that is indirect.

False, high spaciousness factors

T/F : Low spaciousness factors are best.

0.4 to 0.6 seconds

Ideal reverberation time in small classroom is ____ to ____.

1.0 to 1.5 seconds

Ideal reverberation time in auditoriums is ____ to ____.

Voices

Ideal reverberation time in classroom helps maximize ability to hear _____.

True

T/F : Most classrooms have times of one second or more.

Octave

Sounds separated by octave seem more similar than sounds separated by less than an octave.

262.2 Hz

Middle C

523.2 Hz

One octave high

True

T/F : Letters in the musical scale repeat.

True

T/F : Notes with the same letter name (separated by octaves) have fundamental frequencies that are multiples of each other.

Chroma

Notes with the same letter name have the same tone _____.

Gestalt Principles

Heuristics that help to perceptually organize stimuli.

Location

Single sound source tends to come from one location and to move continuously.

Timbre & Pitch Similarity

Similar sounds are grouped together.

Bregman & Campbell Experiment

Stimuli were alternating between high & low tones.

• When stimuli are played quickly, the listener hears two streams ; one high and one low.

Deutsch Experiment

Scale illusion or melodic channeling.

• Perceptual heuristic that sounds with the same frequency come from the same source, which is usually true in the environment.

Warren et al. Experiment

Tones were presented interrupted by gaps of silence or by noise.

• Silence Condition : Sound stopped during the gaps.

  • Noise Condition : Perception was that the sound continued behind the noise.

Auditory Stream Segregation

Bregman & Campbell Experiment, Deutsch Experiment

Good Continuation

Warren et al. Experiment