Hearing Science Exam 2

CSD 850

Absolute Threshold

Lowest sound detectable 50% of the time

Difference Threshold

Smallest detectable change in a sound property

Terminal Threshold

Point of pain or discomfort

Minimal Audible Filed (MAF)

Free-field presentation; includes pinna effects, room reflections —> better thresholds

Minimum Audible Pressure (MAP)

Via earphones/headphones. Excludes pinna effects —> worse threshold

Responses

Hit, Miss, False Alarm, Correct Rejection

Hit

Tone presented, listener pressed button

Miss

Tone presented, not acklowedged

False Alarm

No tone presented, listener press button

Correct Rejection

No tone, no button press

Signal Detection can be affected by…

Sensitivity and decision criterion (observer bias). Separates perceptual ability from response bias.

Better detection at what time presentation

About 200-300 ms

Threshold … as duration ….

Threshold gets better as duration increases. When a sound lasts longer, it is easier to hear. This happens because the ear integrates sound energy over time (temporal/energy summation)

Classical Psychoacoustic Measurement Methods

Method of limits, method of adjustment, method of constant stimuli

Method of limits

The sound level is changed gradually until the listener’s response changes (e.g., from “no” to “yes”). This is done in ascending and descending series.

Method of Adjustment

The listener adjusts the stimulus intensity themselves until it’s just audible (or just inaudible).

Method of Constant Stimuli

Preselected sound levels (some below, at, and above threshold) are presented in random order many times. The % of “yes” responses at each level is plotted to find the 50% detection point.

Adaptive Methods

Up-down (Staircase), Bekesy Tracking, Forced-Choice Adaptive Procedures

Up-Down (staircase) Method

If the listener hears the sound, the next trial is softer; if not, it’s louder. Threshold = average of reversals.

Bekesy Tracking

The listener continuously holds a button while hearing a tone that gradually changes in level — threshold = average of “on/off” crossings.

Forced-Choice Adaptive Procedures

The listener chooses between intervals (e.g., 2AFC — two-alternative forced choice). Minimizes guessing bias.

Cochlea acts as??

Bank of bandpass filters

Critical Bandwidth

Frequency range over which energy integrates to mask a tone

Power Spectrum Model

Masking occurs when noise energy within the critical band equals tone energy

Equivalent Rectangular Bandwidth (ERB)

Refines bandwidth estimation; increases with frequency

Notched-Noise Method

Estimate the shape and width of the auditory filter indirectly using masking noise with a spectral notch around the signal frequency. Present a broadband noise masker with a notch (gap) centered around the signal frequency.

• Keep the total noise power constant, but vary the width of the notch.

• Measure how the signal threshold changes as the notch width increases.

Psychoacoustic Tuning Curves

Find the lowest level of a masker (at various frequencies) that just masks a fixed low-level tone (the probe signal). Present a signal tone at a constant frequency and low level (e.g., 1 kHz at 10 dB SPL).

• Present maskers at different frequencies.

• Adjust the masker level at each frequency until the listener can just not hear the signal.

• Plot masker level (y-axis) vs. masker frequency (x-axis) → this gives the tuning curve.

Simultaneous Masking

Masker and signal overlap

Upward Spread

Low-frequency masker masks higher frequencies (BM mechanics)

Forward Masking

Masker —> delay —> signal

Backward masking

Signal before masker (less effective)

Comodulation Masking Release

Threshold improves when modulations are correlated across frequency bands —> common modulation aids grouping

Energetic Masking

Cochlea overlap

Informational Masking

Perceptual confusion

Loudness level

Phon, equal-loudness contours

Loudness (sone)

Ratio scale (steven’s law)

Recruitment

Faster loudness growth (SNHL)

Hyperacusis

Intolerance to moderate sounds

Dynamic Range

UCL minus threshold

Interaural Time Difference (ITD)

Low Frequencies <1500 Hz

Interaural Level Difference (ILD)

High frequencies >1500 Hz

Cone of Confusion

Identical ITD/ILD pairs —> can be resolved by head movements & spectral pinna cues

Localization

Real-space direction

Lateralization

Headphone perception

Precedence (Haas) Effect

First-arriving sound dominates localization despite echoes. <1 ms one sound. 1-30 ms first sound. >30 ms separate sources, echo

SOC

ITD (MSO) & ILD (LSO)

Pitch scale

Mel

Place Theory

BM location of activation

Temporal Theory

Phase-locking up to 4-5 kHz

Missing Fundamental

Pitch heard even if fundamental frequency is absent (brain infers the periodicity)

Vowels are determined by:

Formant frequencies, F1 and F2

F1

Decreases with increases tongue height

F2

Increases with tongue frontness

/a/

Has high F1

/i/

Has high f2

Consonants are determined my

Manner of articulation, Place of articulation, and Voicing

Voicing

Vocal fold vibration /p/ vs /b/

Place of Articulation

Bilabial /b/, alveolar /t/, velar /g/

Manner of articulation

Stop /k/, nasal /n/, fricative /f/, affricate /dʒ/

Acoustic Cues

Voice Onset Time (VOT) and bursts

VOT

The time interval between the release of a stop consonant (like /p/, /t/, /k/) and the onset of vocal fold vibration (voicing).

Bursts

The spectral (frequency) characteristics of the noise burst produced when air is suddenly released after a stop closure (like /p/, /t/, /k/). Different places of articulation create bursts at different frequency ranges:

Coarticulation

Neighboring sounds influence acoustic patterns

Bottom-up

Use of acoustic cues

Top-down

Using linguistic knowledge & context

Lateralization

Primarily left hemisphere, but it can vary based on your dominant hand. Those who are left hand dominant can be right hemisphere or bilateral.

Auditory Scene Analysis (ASA)

The process of grouping sounds from the same source and separating sounds from different sources.

Temporal & Frequency Proximity

• Sounds close in time/frequency group together.

• Large frequency gaps or fast alternations → segregation.

Similarity

• Grouping by pitch, timbre, location, or loudness.

• Dissimilarity promotes segregation (e.g., male vs. female voice).

Closure

• Perceive continuity through interruptions (phonemic restoration).

• E.g., hearing speech as continuous through noise.

How does VOT (Voice Onset Time) differentiate /b/ vs /p/?

• In /b/, vocal folds start vibrating almost immediately after lip release → short VOT.

• In /p/, vocal fold vibration is delayed → longer VOT.
  The auditory system uses this timing cue to distinguish voiced from unvoiced stops.

How does forward masking relate to neural adaptation?

When a sound (masker) makes it harder to hear another sound that follows shortly after. After the masker, auditory nerve fibers are temporarily less responsive due to neural fatigue/adaptation.

• This reduces their firing rate for subsequent sounds → higher thresholds for the target sound.

• The closer in time the target is to the masker, the stronger the masking effect.

How does critical bandwidth affect tone detection in noise?

The critical bandwidth (CB) defines the frequency range over which energy contributes to masking a tone. Only noise within the tone’s critical band effectively masks the tone.

• Increasing noise bandwidth within the CB → more masking (threshold rises).

• Increasing noise bandwidth beyond the CB → no further effect (threshold saturates). Tone detection depends on noise energy inside the auditory filter tuned to that frequency — not on total noise bandwidth