5-7 Hearing Science, Exam 2 Hearing Science

3 auditory perceptual tasks

auditory sensitivity (detection)

auditory discrimination

auditory identification (recognition)

auditory detection

ability to distinguish between the presence and absence of sound (to hear or not hear a sound)

psychoacoustics definition

the relationship between the physical feature of sound and auditory perception

Acoustics Definition

study of the physical properties of sound

Psychology definition

study of the brain and how someone perceives the surrounding environments and stimuli

auditory discrimination

The ability to tell the difference between one sound and another sound (are the sounds the same or different?)

Auditory Identification (Recognition)

the ability to label or recognize what a sound actually is (i.e., identifying and understanding speech)

Psychoacoustics Method of Limit definition

A technique used to measure a person's sensory threshold by gradually increasing or decreasing the intensity of a stimulus until the person's response changes

Method of limit ascending

You start below the person's threshold (so they can't hear it) and increase the intensity step-by-step until they indicate that they can hear the sound

The point at which they first hear the sound estimates the threshold.

Method of limit descending

You start above threshold (clearly audible) and decrease intensity step-by-step until the person indicates they cannot hear the noise

The point where they lose perception is another estimate of the threshold.

Method of limits adaptive

The test changes direction depending on the listener's response.

Example: If they say they hear it, the next step is softer; if they don't hear it, the next step is louder.

This helps quickly "zero in" on the exact threshold.

Fixed Step Size

Each increase or decrease in sound intensity is the same amount (e.g., 5 dB, 2 dB).

Why do we use fixed step size?

Keeps the procedure consistent.

Used to gradually approach the threshold from both directions.

Even adaptive methods often use fixed step sizes for each adjustment.

Method of limits threshold

You collect the intensity levels at several reversal points.

Then you average the reversal values.

Method of limits reversal

occurs when the direction of the stimulus changes

Example: You're making the tone softer (descending) and the listener stops hearing it. Next trial, you make it louder (ascending).

method of constant stimuli

psychophysical technique where several predetermined stimulus intensities are repeatedly presented in random order, and the observer's yes/no responses are used to plot a psychometric function and determine the detection threshold.

psychometric function

A curve that shows how a person's probability (percent) of detecting or correctly responding to a stimulus changes as the stimulus intensity increases.

psychometric function features

There is an equal number of stimuli at each level

threshold is a certain percentage point

3 scaling methods

direct scaling, ratio scaling, magnitude scaling

direct scaling

-Directly establishes the correspondence between physical sounds and their perception.

-Loudness and pitch

ratio scale

numbers a person assigns to a stimulus reflect true numerical ratios

compared to the reference sound

magnitude scale

numeric rating system where a person assigns numbers to describe how strong a stimulus feels, so bigger numbers mean a stronger perceived intensity.

No reference sound provided

auditory masking

interference that one stimulus causes in the perception of another stimulus

what is masking measured as?

masking is measured in percentage

Amount of masking

masking efficiency - how well the masker can block auditory perception

Masking efficiency formula

amount of masking = score in Q - Score in noise

What can be a masker?

Any unwanted sound is a masker (any sound that isn't your target signal)

amount of masking depends on

timing of the masker, its intensity, frequency, and bandwidth

frequency and level of the signal and masker

tonal masker

pure tone is the masker that influences masking by noise level (more noise, more masking) and frequency (in general broader the noise frequency, the more masking there is, but it depends on the signal)

tonal masking occurs when

a loud, pure tone (the masker) makes a softer, nearby tone (the target) inaudible

Thresholds of tonal detection with tonal masker

masking efficiency is dependent on the intensity level and frequency of the tonal masker

psychoacoustic tuning curve

graphical representations of an auditory system's frequency selectivity, showing the masker level needed to mask a fixed signal frequency across a range of masker frequencies.

Auditory filter

a theoretical model of how the human ear, specifically the cochlea, separates sounds into different frequency bands

Frequency-dependent masking suggests that

only those frequencies close to the signal frequencies close to the signal frequency are effective in masking

Critical Band of the Auditory Filter

auditory system filters out noise frequencies far away from the signal frequency

Signal Frequency

Rate at which a signal oscillates (repeats over time), measured in hertz, determines pitch

Our auditory system is composed of a set of filters tuned to

different frequencies

Bandwidth of auditory filter

measured by a notch noise method

affected by signal level and hearing status

Equivalent Rectangular Bandwidth (ERB)

used to estimate the size/width of the auditory filter

ERB formula

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Auditory filter determines our

frequency selectivity

frequency selectivity

the auditory system's ability to respond differentially to different frequencies and bands of frequencies

Narrower auditory filter bandwidth =

better frequency selectivity

signal level

The higher the signal level, the broader the bandwidth of the auditory filter

What is measure-notch noise?

A method for testing a listener's ability to detect a pure-tone signal within a masker noise.

What is created in the masker noise during measure-notch noise testing?

A spectral 'notch,' or gap, around the signal frequency.

What is varied in measure-notch noise testing?

The width of the notch created in the masker noise.

auditory filter bandwidth's relationship with frequency selectivity

a narrow bandwidth results in high frequency selectivity, and a wide bandwidth results in low frequency selectivity

loudness definition

attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud

how to measure loudness

matching and scaling

matching method

Listeners are asked to adjust the level of the target sound to match the loudness of the reference sound, has equal loudness contour

matching method reference sound

1 kHz tone at 40, 50... dB SPL

Equal Loudness Contours

graph with presentation level on the y-axis and frequency on the x-axis, showing graph lines connecting points of equal perceived loudness

loudness growth function

describes how our perception of loudness changes as the intensity (level) of a sound increases

Scaling method

listeners are asked to scale the loudness level of the target sound relative to the loudness of the reference sound

scaling method reference sound

1 kHz tone at 40 dB SPL defined as 1 sone

sone

everytime you increase the sound db by 10 it will double the sone (40db →50db →60db = 1sone→2sone→4 sone)

loudness growth function

For sounds above 40 dB, loudness doubles when the sound level is increased by 10 dB

loudness recruitment

for those with hearing loss, the increase of volume is much steeper (increases of 10dB might be perceived as 8 times louder for someone with hearing loss)

factors affecting loudness

intensity, frequency, bandwidth, duration

loudness summation

the phenomenon where the perceived loudness of a sound increases when heard with both ears (binaural) compared to a single ear (monaural), or when the bandwidth of a sound stimulus is increased while its power is held constant (spectral)

pitch definition

attribute of auditory sensation in terms of which sounds may be ordered on a musical scale

how to measure pitch

matching and scale methods

pitch matching method

reference sound: a tonal sound

Listeners are asked to adjust the frequency of the reference sound to match the pitch of the target sound

pitch scaling method

Listeners are asked to scale the pitch value of the target sound relative to the pitch value of the reference sound (1 kHz)

pitch scaling method reference sound

1 kHz tone defined to have a pitch at 1000 mel

scaling method results are hard to measure due to

the complexity of pitch

pitch of complex sounds

- missing fundamentals - complex tones

listeners can perceive a pitch for complete tones that do not have any spectral components at the perceived pitch

two theories of complex sound pitch

envelope-periodicity theory (temporal periodicity) and spectral location theory

envelope periodicity theory

periodicity of the complex sound waveform

Spectral-location theory

spectral distance between tones

2 components of the auditory system

peripheral auditory system (outer, middle, inner ear)

central auditory system (auditory brainstem and auditory forebrain)

3 components of the peripheral auditory system

Outer ear, middle ear, and inner ear

Anatomy of the outer ear

pinna and external ear canal

Physiology of the outer ear (4 functions)

i. Collect sound

ii. Sound pressure gain (amply middle frequencies 1-5 kHz)

iii. Sound localization

iv. Protection of the tympanic membrane

Sound pressure gain

peaked around 2.5 kHz

primary contribution from the concha and the outer ear

This gain is crucial for hearing sensitivity in the speech frequency range.

What is sound localization?

The process by which the location of sound is determined.

What cues are used for localizing sound?

Intensity and phase (time) difference.

pinna anatomy

visable, cartiligenous part of the ear

pinna physiology

sound localization in the midplane

acts as a funnel to direct sound waves towards the ear canal

external ear canal anatomy

a tube leading to the eardrum

external ear canal physiology

Provides an acoustic resonance effect, leading to sound pressure gain (peaking around 2.5 kHz)

middle ear anatomy

tympanic membrane

tympanic muscles

auditory ossicles

eustachian tube

Middle Ear Physiology

sound transmission and protection of hearing

tympanic membrane anatomy

eardrum

tympanic membrane physiology

Transduces acoustic energy signals (air molecule vibration) into mechanical motion.

auditory ossicles anatomy

malleus, incus, stapes

auditory ossicles physiology

Transduces the mechanical motion of the TM to fluid motion in the cochlea

Amplifies sound intensity across frequencies

At what frequency do the auditory ossicles provide peak amplification?

1000 Hz

How do the auditory ossicles transduce sound?

through transducing the mechanical motion of the ossicles to fluid motion in the cochlea (from the stapes moving in and out of the oval window)

Sound transfer functions of the middle ear

sound intensity amplified across frequencies with peaked amplification at 1000 Hz

Problem of sound transmission - What happens when vibration of sound wave transfers from the tympanic membrane in the air to fluid-filled cochlea?

Most of the acoustic energy will be reflected because the difference of acoustic impedance between the two sound media.

Solutions to the sound transmission problem

impedance mismatch problem - increase pressure/force at the oval window

sound mismatch issue

During the change between the ear drum and the fluid motion of the cochlea, the two mediums cause impedance mismatching. The sounds are mostly reflected (bouncing off an oval window).

Three mechanisms for impedance mismatch problem

area ratio, lever system, buckling of eardrum

Area Ratio (hydraulic affect)

Sound vibrates the large eardrum, but this force is concentrated onto the much smaller stapes footplate, greatly increasing pressure (approx. 18x gain)

lever system

The malleus and incus act as a lever, multiplying the force by about 2.1 times.

Buckling of ear drum

buckling motion increases the force transmitted to the middle ear's ossicles, effectively amplifying the sound pressure

acoustic reflexes

stapedius and tensor tympani (middle ear muscles) contract to lower sound transmission in the middle ear after receiving intense sounds

acoustic reflexes purpose

protects inner ear from intense sounds