Hearing Science Final

Define sound

Fluctuations in air pressure across time

Define hearing

Process that transforms sound waves into neural signals that can be interpreted by our brain

Define hearing science

The relationship between the physical properties of sound and the sensation they produce

Identify parts of a sounds waveform

Sounds is a longitudinal compression wave represented as a sine wave

• Peaks are pressure condensations

• Zero is resting pressure

• Troughs are pressure refraction as troughs

Identify the parts of this graph (peaks, etc.)

Calculate the frequency of a sine wave given it's frequency

F = 1/T

Understand the relationship between the waveform and magnitude spectrum of a sine wave

Frequencies are lines across the x-axis with height of amplitude on the y-axis

Identical magnitude spectra for sine waves with the same amplitude and frequency

One line is a single-frequency tone

Multiple lines is a complex tone

Identify the essential parameters needs to represent a sinusoid of a sine wave

Frequency, Amplitude, Phase

Identify the essential parameters needed to represent the magnitude spectrum of a sine wave

Frequency, Amplitude, and NOT Phase

Distinguish between sounds with a continuous spectrum (e.g., white noise) and those with a discrete spectrum (e.g., sine waves, complex tones)

Continuous spectrum (e.g., white noise): Contains energy at all frequencies within a certain range

Discrete spectrum (e.g., sine waves, complex tones): Contains energy at specific, isolated frequencies

Understand the major differences between a complex tone and a pure tone

Pure tone has one frequency component

Complex tone has more than one frequency component (typically harmonic)

Understand the relationship between complex tone’s period and the period of its fundamental component

They are identical

Describe the spacing between harmonics in complex tones

Constant

Contrast the differences between low-pass, high-pass, and band-pass filters

Low-pass filter removes high frequencies

High-pass frequencies removes low frequencies

Band-pass filter removes frequencies outside of its band width

Bandwidth is ____ from peak (50% relative power)

-3dB

Explain why dB is useful in hearing science

Compressive: The human ear is sensitive to 10¹³ units of intensity on a linear scale; a logarithmic scale condenses that range to 130 decibels

Closer to human sensation: The logarithmic scale more closely approximated the way human ears perceive loudness, Each increase in decibel corresponds roughly to an equal perceived growth in loudness, even though the sound power differences are large

10-fold increase in pressure =

+20dB

100-fold increase in pressure =

+40dB

1000-fold increase in pressure =

+60dB

Double the pressure =

+6dB

Quadruple the pressure =

+12dB

Understand the Steven’s Power Law

Describes the sensory growth as compressive with increasing stimulus intensity

Identify the physical properties of a sound that affect its loudness

intensity

Frequency: Equal loudness contours equal loudness contours

Duration: “Critical duration”

Identify the physical properties of a sound that DO NOT affect its loudness

Phase

Use equal loudness contours to compare the loudness of pure tones at different frequencies and SPLs

Find the intersection of frequency (x-axis) and SPL (y-axis) then report the hearing threshold of the curve

Equal loudness contours

Flatter at higher loudness levels — less of a difference in perceives loudness as a function of frequency

Rate of growth of loudness differs for tones of different frequencies

Describe the roles of the outer ear in audition

Pinna: Significantly modifies the incoming sound, at high frequencies, which is important for sound localization

Ear Canal: Resonance frequency around 3kHz

Describe the role of the middle ear in audition

The lever action of the ossicular chain amplifies incoming sounds

Understand properties of the basilar membrane (hint: tonotopically organized)

Located in the inner ear

The place of maximum displacement depends on stimulus frequency

• High frequencies excite the base while low frequencies excite the axis

• Nonlinear response

Differentiate between types of hair cells

Understand Fletcher’s critical-band experiment, identifying the independent variable and the dependent variable

Purpose: Measure bandwidth of auditory filters

Independent Variable: Making noise bandwidth

Dependent Variable: Signal amplitude

Control: Signal frequency, Noise amplitude at threshold

Determine the critical bandwidth of an auditory filter centered at a specific frequency from experimental results

Critical bandwidth graph

• “Knee point”

  • 400 Hz

Identify the dependent variable and independent variable in the tone-on-tone masking experiment

Purpose: Measure the shape of the auditory filter across frequencies (effectively basilar membrane)

Independent Variable: Masker frequency

Dependent Variable: Masker amplitude at threshold

Control Variables: Signal amplitude at threshold, Signal frequency

Predict which single-frequency pure tone will mask a target tone at the lowest level

Best masking → Worst masking

Same frequency, Closest frequency, Lowest frequency

Identify factors influencing the narrowness of auditory filters

Frequency

SPL: More = wider

Hearing loss

Compare the effectiveness of different types of masking

Best Masking → Worst Masking:

Forward fringe

Backward fringe

Forward

Backward

Understand central masking including how dichotic listening conditions differ between backward and forward masking

Central masking can occur during dichotic listening conditions due to a central mechanism

Backward masking is an example that can occur centrally

Understand how sound integration changes until the critical duration

For durations up to the critical duration, sounds with longer duration are detected more easily

Identify the parameters of amplitude modulation

Modulation depth or amplitude modulation (AM)

Modulation rate or frequency modulation (FM)

Understand temporal modulation transfer functions (TMTFs)

The plot of AM detection thresholds as a function of modulation rate

Threshold is plotted as modulation depth in dB with low (good) values at the bottom

What does a TMTF “cut-off” AM implicate?

The auditory system acts like a low-pass filter when it comes to temporal fluctuations in sounds, with a cutoff frequency (3dB down point ) around 50-60 Hz

We can follow fluctuations up that modulation rate fine, but at higher rates, we don’t follow as well

Identify the independent and dependent variable in experiments measuring TMTFs

Independent variable: Modulation frequency

Dependent variable: Modulation depth at the threshold

Control variables: Carrier amplitude at the threshold, Carrier frequencies at the thresholds

Explain which frequency range the temporal theory can explain pure-tone pitch perception

Low frequencies under 1000 Hz

Use phase-locking mechanism

Explain which frequency range the place theory can explain pure-tone pitch perception

Works for low and high frequencies

Best for high frequencies above 2000 Hz

Calculate the frequency of beats generated by two sine waves

Difference in Hz

Beats (500,450) = 50

Describe how neurons phase-lock to the fine structure for resolves harmonics and to the temporal envelope (beating frequency) for unresolved harmonics

Two mechanisms for complex-tone pitch perception

• Pattern matching of resolved harmonics works for low-frequency harmonics

• Temporal envelope coding of unwanted harmonics: works for high-frequency harmonics

Understand with which type of harmonics the temporal code is dominant for the perception of complex-tone pitches

Unresolved harmonics

Identify the three main aspects of spatial perception

Azimuth angle

Elevation angle

Distance

Identify the aspect of spatial perception to which humans are more sensitive

Azimuth angle

Identify the major cues for azimuth angle perception

Intramural time difference (ITD)

Intramural level difference (ILD)

Identify the major cues for duplex theory

ITD - low

ILD - high

Explain at which frequency ILD is biggest and the primary reason for ILD

Head, above 2000 Hz

Head shadow effect

Explain for which frequency range ITD is most effective for sound localization and the primary reason for ITD

Low, under 1000 Hz (exists for high, but not effective)

Phases differences from path length

Identify what auditory cues are important for distance perception

Intensity cues (attenuation over distance): Gets quieter with more distance

Reverberation cues: Important for distance

Explain how human sound localization resolves front-back confusion

Identify examples of organizing principles

Onset timing: Sounds starting at different times likely from different sources

• Ex. Forward fringe masking

Location: Single sound source comes from one location

• Ex. Bilateral masking level difference (BMLDs)

Coherent temporal changes: Matched AM and/or FM changes over time

• Ex. Comodulation Masking Release (CMR)

Gestalt principles in audition: Similarity

Similar pitches heard as one stream; different pitches as separate stream

Gestalt principles in audition: Proximity

Sounds close in time or frequency tend to group together

Gestalt principles in audition: Continuity

Sounds perceives as continuing behind interrupting noise

Gestalt principles in audition: Common fate

Sounds changing together (in amplitude, frequency) grouped together

Identify the primary determinant of a speaker’s pitch

Acoustic source, i.e., glottal pulses from vocal fold vibrations

Identify the major acoustic properties determining English vowels

Formant frequencies (primarily the first 2)

Identify the main attributes for English consonant classification

Place, Manner, Voice

Understand aspects of the Motor Theory of speech perception

Speech perception involves reference to articulation

Specialized neural module translates acoustic signals to articulatory gestures

Analysis-by-synthesis mechanism

Evidence: Categorical perception, McGurk effect, duplex perception

Unilateral vs. Bilateral

One vs. both

Congenital vs. Adventitious

Congenital: At birth

Adventitious: Acquired after birth

Hearing loss based on time course

Acute vs. Chronic

Temporary vs. Permanent

Progressive vs. Fluctuating

Conductive hearing loss

Problem in outer/middle ear

Constant threshold elevation across frequencies

Air-bone gap present on audiogram

Sensorineural hearing loss

Problem in cochlea or auditory nerve

Often worse at high frequencies

No air-bone gap

Mixed hearing loss

Both conductive and sensorineural components

Air-bone gap, but less than conductive hearing loss

Identify the major signal-processing strategy used in modern hearing aids

Amplification: Making sounds louder

Filtering: Emphasizing certain frequencies

Compression: Reducing dynamic range

• High gain for low intensities

• Low gain for high frequencies

• Addresses recruitment problem

Linear signal processing

Constant gain regardless of input level

Non-linear signal processing

Gain changes with input level

Automatic Gain Control (AGC)

Multi-channel processing for different frequency regions

Identify the problem with linear signal processing in hearing aids and the solution

Problem: Loud sounds become uncomfortable

Solution: Peak clipping, but this causes distortion

Understand the function of cochlear implants

Bypass damaged hair cells to stimulate the auditory nerve directly with electrical signals

Identify the signal-processing component unique to cochlear implants

Use vocoding

Explain the difference in candidacy between hearing aids and cochlear implants

HA: Moderate sensorineural hearing loss, unilateral or bilateral

CI: Bilateral severe-profound sensorineural hearing loss, limited benefit from hearing aids, no medical contradictions

Cochlear implants in adults and children

Adults: Poor speech recognition, telephone use different

Children: 12+ months, lack of benefit from hearing aids

Explain the main differences between a prescription hearing aid and OTC hearing aid

Prescription HA: require a hearing test, tailored to your needs

OTC HA: Not fit by an audiologist, for mild-moderate hearing loss

Describe the challenges of using untrained interpreters in audiology settings

Misinterpretations, inaccuracy in communication

Understand that speech in background noise involves multiple neuro-cognitive processes and neurofeedback training of selective attention may provide an effective rehabilitation strategy

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