Hearing Science

Binaural cues

ITD’s and ILD’s

ITDs

More effective for low frequencies (<1600 Hz)
▪ compare the arrival times of phase-locked responses
due to path length differences
▪ exist for all frequencies equally, but they are confusing
for high frequencies.
▪ are greatest for sound locations around 90 degrees in
azimuth, and can be as large as 0.65ms.

ILDs

▪ More effective for high frequencies (>1600 Hz)
▪are caused by head shadow effect for wavelengths
greater than the diameter of the head
▪is 0 for 0 degrees, greatest for 90 degrees

duplex theory

Use ITDs for low frequencies and ILDs for high frequencies
• Poor performance in the middle (1500 Hz)

minimal audible angle

Threshold for detecting a change in spatial location of a sound
source (JND for spatial location, Mills, 1958)
• Expressed in degrees, smaller/narrower is lower threshold (more
sensitive)
• Best directly in front, then back, worst at sides
• Frequency dependency is correlated with Duplex Theory

font and back confusion

same ITDs and ILDs resolved by pinna cues and head movements

space perception of azimuth angle

binaural cues, duplex theory, minimal audible angle, front and back confusion

space perception of elevation

based on monaural spectral cues, not interaural differences, cone confusion, less accurate than azimuth angle

cone confusion

sources with same ITDs and ILDs, head-related transfer functions (HRTFs) created by pinna, head, and shoulders

perception of distance

intensity cues reverberation

intensity cues

attenuated over distance

reverberation cues

direct/indirect sound ratio; time delay between direct sound and reflections

auditory scene analysis

process of separating sound sources in the environment

auditory scene analysis

its organizing principle:

onset timing, location, coherent temporal changes

onset timing

sound starting at different times likely from different sources

onset timing

forward fringe masking

location

single sound source comes from one place

location

bilateral masking levels (BMLDs)

coherent temporal changes

matched AM and/or FM changes over time

coherent temporal changes

comodulation masking release (CMR)

gestalt principles in audition

similarity, proximity, continuity, common fate

similarity

similar pitches heard as one stream; different pitches as separate streams

proximity

sounds close in time or frequency tend to group together

continuity

sounds perceived as continuing behind interrupting noise

common fate

sounds changing together (in amplitude, frequency) grouped together

speech perception of vowels

source filter theory and vowel production

source

larynx sound production, acoustic, aerodynamic

larynx

source of vowels and voiced consonants, determines pitch

acoustic

glottal pulse from vocal fold vibrations

aerodynamic

air pressure and flow from lungs

filter

the vocal tract and articulators filter the vocal vibrations through resonance

filter

determines speech sound category and timbre

vowel production

determined by formants; relative formant positions more important than absolute frequencies

F1

tongue height

F2

tongue advancement

consonant production

place and manner of articulation, voicing

place of articulation

where constriction occurs

manner of articulation

how air is constricted

voicing

whether vocal folds vibrate during production

acoustic cues

voice onset time, burst frequency, formant transitioning

voice onset time

time between release burst and vocal fold vibration

voice onset time

short lag (0-20ms): voiced sounds

long lag(80-100ms): voiceless sounds

burst frequency

varies by place of articulation

formant transitions

movement of formants into and out of consonants

formant transitions

locus concept

coarticulation

1. Speech sounds affected by neighboring sounds
2. Creates context-dependent acoustic cues
3. Leads to lack of invariance problem

motor theory

1. Speech perception involves reference to articulation
2. Specialized neural module translates acoustic signals to articulatory
gestures
3. Analysis-by-synthesis mechanism
4. Evidence: Categorical perception, McGurk effect, duplex perception

hearing impairment

based on: ears involved, onset, time course

ears involved

unilateral vs bilateral; hearing impairment

onset

congenital vs adventitious; haring impairment

time course

acute vs chronic, temporary vs permanent, progressive vs fluctuating; hearing impairment

hearing sensitivity loss

conductive, sensorineural, mixed

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

signal processing

amplification, filtering, compression

amplification

making sounds louder

filtering

emphasizing certain frequencies

compression

reducing dynamic range

compression

▪ High gain for low intensities
▪ Low gain for high intensities
▪ Addresses recruitment problem

types of processing

linear and nonlinear

linear

constant gain regardless of input level; problem and solution

problem

loud sounds become uncomfortable; linear

solution

peak clipping (causes distortion); linear

nonlinear

gain changes with input level

nonlinear

automatic gain control, multi-channel processing for different frequency regions

cochlear implants

Surgically implanted device that bypasses damaged hair cells to
stimulate auditory nerve

external and internal

cochlear implants components

external

speech processor, headpiece, battery; cochlear implants

internal

electrode array, receiver-stimulator; cochlear implants

signal processing

vocoder, fewer channels

vocoder

divides sound into frequency bands

poorer frequent selectivity

fewer channels equal what