Hearing Science Midterm 3

Perception of Azimuth Angle

Binaural cues, Duplex Theory, Minimum Audible Angle, Front and Back Confusion

Intramural Time Difference (ITD’s)

More effective for low frequencies (less than 1600 Hz)

Intramural Level Difference (ILD’s)

More effective for high frequencies (greater than 1600 Hz)

Duplex Theory

ITD’s for low frequencies and ILD’s for high frequencies

Minimum Audible Angle (MAA)

Best in front - 0, then behind - 180, worst at sides - 90

Changes with frequency, worst at 1500 Hz, supports duplex theory

Front & Back Confusion

Same ITD’s and ILD’s, resolved by pinna cues and head movements

Perception of Elevation

Monoaural Spectral Cues

Head Related Transfer Function (HRTF) created by pinna, head and shoulders

Cone of Confusion

Cone of Confusion

Can not differentiate location when ITD’s and ILD’s are the same

Solved by head movement with HRTF

Perception of Distance

Intensity Cues

Reverberation Cues: Direct/Indirect sound ration, time delay between direct sounds and reflections

Auditory Scene Analysis

Process of separating sound sources in the environment

Organizing Principles of Auditory Scene Analysis

Onset Timing: Sounds starting at different times are likely from different sources

Location: Single sound source comes from one location

Coherent Temporal Changes: Comodulation Masking Release (CMR)

Gestalt Principle - Similarity

Similar pitches heard as one stream, different pitches heard as separate streams

Gestalt Principle - Proximity

Sounds close in time or proximity are often grouped together

Gestalt Principle - Continuity

Sounds perceived as continuing behind interrupting noise

Common Fate

Sounds changing together in amplitude and frequency are grouped together

Source Filter Theory

Source: Larynx and glottal pulse from vocal fold vibrations

Filter: Vocal tract shape and articulators

Vowel Formant 1

Tongue Height

Vowel Formant 2

Tongue advancement - forward/backward

Vowel perception is impacted by…

Resonance of vocal tract, formants and positions (not frequencies)

Voice Onset Time (VOT)

Time between release of burst and vocal fold vibration

Short Lag

Voiced Sounds (0-20 ms)

Long Lag

Voiceless Sounds (80-100 ms)

Formant Transitions

Movement of formants into and out of consonants - Locus Concept

Coarticulation

Speech sounds affected by neighboring sounds

Creates context-dependent acoustic cues

Leads to lack of invariance problem

Hearing Impairment

Unilateral vs Bilateral

Congenital vs Adventitious

Acute (quick onset & short lived) vs Chronic (develop slowly & last longer)

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

Mixed Hearing Loss

Has components of both conductive and sensorineural hearing loss

Hearing Aids - Signal Processing

Amplification

Filtering: Emphasizing certain frequencies

Compression: Reducing dynamic range

Hearing Aids - Compression

High gain for low intensities

Low gain for high intensities

Addresses recruitment problem

Hearing Aids - Linear Processing

Constant gain regardless of input level

Problem: Loud sounds become uncomfortable

Solution: Peak clipping

Hearing Aids - Nonlinear Processing

Gain changes with input level

Automatic Gain Control (AGC)

Multi-channel processing for different frequency regions

Cochlear Implant Components

External: Speech processor, headpiece, battery

Internal: Electrode array, reciever-stimulator

Cochlear Implants - Signal Processing

Vocoder: Divides sound into frequency bands

Fewer Chanels = poorer frequency selectivity

Components of Motor Theory

Speech perception involves reference to articulation

Specialized neural module translates acoustic signals to articulatory gestures

Analysis by synthesis mechanism

Evidence: categorical perception, McGurk effect