CSD 2230
INTRODUCTION TO HUMAN
COMMUNICATION DISORDERS
Normal Sound Perception, Speech
Perception, and Auditory
Characteristics at the Boundaries of the
Lifespan
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The Perception of Sound
What do we hear when
we listen to a
sound??
The Perception of Sound
Psychoacoustics is a
branch of
experimental
psychology
interested in these
questions
Overview of Perception
Although the physical
characteristics used to
measure sounds are
objective, how we
experience sounds is
subjective
n
Objective Characteristics
•
•
•
Intensity
Frequency
Duration
Subjective Characteristics
Pitch
Questions to Ask
What are the limits of our ability to sense
sound?
 How do our subjective impressions of
sounds change as we change the
physical dimensions of sound?

Overview of Perception

How we experience
sounds is subjective

Listeners are variable
in their responses
Hearing Acuity
What are our limits in
detecting sounds?

Audibility and
detectability

Frequency and
intensity restrictions
Normal Auditory Sensitivity
Normal hearing listeners
are capable of detecting
sounds within a range of
1 Hz up to about 20,000
Hz
Sensitivity is NOT equal
across this range
Best sensitivity is between
1000-5000 Hz
As the frequency of the
sound moves above or
below this range,
sensitivity gets
progressively worse
Auditory Area
n
The useful range of hearing for any individual is
taken to be the area between the person’s
absolute threshold and the threshold of feeling
The Normal Auditory Area



Useful frequency
range is between 20
and 20,000 Hz
Dynamic range is
widest between 1000
and 5000 Hz
Widest range is 120
dB
Intensities of Common Sounds
Thresholds

Absolute sensitivity--the minimum
intensity at which a listener can
distinguish sound from silence
ü Detection

Differential sensitivity--the smallest
change in a stimulus a listener is just able
to detect
n Discrimination
Differential Sensitivity for
Intensity


Intensity discrimination
depends on whether
sounds are close to
absolute threshold or far
from threshold
In general, for a wide
range of stimulus
intensities and
frequencies, our
discrimination ability for
intensity is 2 dB or less
Differential Sensitivity for
Frequency

Our resolving power
for frequency isn’t as
good as for intensity

Frequency
discrimination
depends on the
general frequency
range of the two
sounds
Characteristics of Normal
Sound Perception and Speech
Acoustic Cues of Speech
1.
2.
3.
Frequency
Intensity
Temporal
Characteristics
Categorical Perception

Represents an important way in which
speech is processed differently by
humans than other sounds

Illustrated by comparing our ability to
discriminate and identify certain kinds of
sounds
Categorical Perception

Discrimination is the ability to tell if two
sounds are the same or different

Identification is the ability to label a sound
Sounds Perceived NonCategorically
Music
 We can discriminate more than 1000
different notes (pitches) but most of us
can only identify about 7.
 Big difference between what we can
discriminate and what we can identify
n
Sounds Perceived Categorically
n
Speech
n
We can discriminate the same number of
speech sounds (phoneme) that we can
identify
Perception of Some Voiced vs.
Unvoiced Consonants


Discriminating /p/ from /b/, /t/ from /d/, or /k/
from /g/
These are English consonants that are formed
the same way (manner of articulation) and
formed in the same area (place of articulation)
of the vocal tract but differ in terms of whether
the vocal folds are vibrating during production
(voicing)
Voice Onset Time

The difference in these phoneme pairs is in the
timing of when the larynx starts to vibrate during
the production of the consonant
voice onset time (VOT)


Voiced stops have a relatively short VOT
Voiceless stops have a longer VOT
VOT Waveform for a Voiceless
Stop
n
VOT measure for /p/. LO represents the
release of the burst (stop). RO is placed at the
highest point of the first cycle of vocal fold
vibration. Notice the relatively long time interval
between these two points.
VOT Waveform for a Voiced
Stop
n
VOT measure for /b/. LO represents the
release of the burst (stop). RO is placed at the
highest point of the first cycle of vocal fold
vibration. Notice the relatively short time
interval between these two points.
Categorical Perception of VOT
n
Identification functions of a single listener for VOT
continuum from /d/ to /t/ in 11 ms steps.
Neat….Huh???
The
big question is:
Are we born with this
ability to perceive
speech categorically?
Or
Do we eventually learn
to perceive speech
categorically?
Infant Studies
n
Before birth

When do we first
hear?

What do we first
hear?
Infant Studies
n


Acuity after birth
How do we measure
this?
Why is it important to
know ASAP??
Nonbehavioral Measures of
Hearing Acuity

Auditory Brainstem
Response (ABR)

Otoacoustic
Emissions (OAEs)
Behavioral Responses of
Infants and Newborns
n
The auditory responses of infants can be
described in terms of reflexive behaviors
and attentive behaviors
Reflexive Behaviors to Loud
Sounds
Reflexes observed
when loud sounds
are presented to an
infant:
n
n
n
The startle response
The auropalpebral
response
Attentive Behaviors in
Newborns and Infants
n
n
n
n
n
n
Quieting responses
Increase in ongoing
activities
Changes in breathing
rate
Changes in vocalization
Eye widening and
searching
Smiling or changes in
facial expression
Attentive Behaviors in
Newborns and Infants
n
The intensity of sounds needed to elicit these
behaviors depends on the type of sound
n
For speech sounds, these behaviors are elicited
at 60-80 dB SPL
Behavioral Responses of
Infants
n
At around 4 months,
infants start to
demonstrate
behaviors consistent
with localization
Visual Reinforcement
Audiometry
n
The younger infant 4
months-9 months
Visual Reinforcement
Audiometry
n
The older infant 9
months-2 years
Infant Speech Perception



Speech is learned the same
way as any other motor
behaviors
Children DO NOT come into
the world as blank slates
Human infants are born with
the capacity for categorizing
may speech sounds in
specialized ways
Infant Speech Perception
n
Eimas’ studies of the 1970s
Infant subjects 1-4 months old
Stimuli included computer generated speech
sounds that varied in VOT to produce either
/pa/ or /ba/
Responses included a non-nutritive sucking
response
Results suggested that the infants perceived
changes in VOT categorically--just like adults
Infant Speech Perception
n
Werker’s studies of the 1980s:
English speaking infants from 6 months-12 months of age
Stimuli included phonemic contrasts from Salish and Hindi
languages
Responses included a non-nutritive sucking response
Results suggested that the younger infants listening to the nonnative contrasts were able to discriminate these speech
contrasts with good accuracy, but the ability disintegrates
progressively as the child ages
Their ability to discriminate contrasts in their native language
remained high
Three Important Conclusions
Regarding Speech Perception
Development



Infants already come into the world with certain
perceptual capacities for phonetic distinctions
used in the world’s languages
Experience with a particular language leads to
decreased perceptibility of at least some nonnative phonetic contrasts and enhanced
perception of native contrasts
By the end of the first year, the influence of a
particular language is evident in the perception
of non-native speech
Older Adults




Changes in acuity
usually begin around the
third decade of life
Incidence increases
sharply as we age
25%-40% of people over
65 have significant
hearing loss
The figure changes to
90% by the time we
reach our 80s
Hearing Loss and Aging


No clear etiology (cause)
Possible sources include:
•
•
•
•
•
•
•
Noise exposure
Genetics
Vascular disease
Systemic disease
Diet
Pollution
Others
Audiologic Characteristics
Associated with Aging
n
n
Acuity:
Changes in pure tone
sensitivity (absolute
thresholds) among
older adults emerges
gradually as age
increases.
Changes in Detection as a
Function of Age and Gender
n
1)
2)
Two trends are clear from these data:
Both males and females exhibit a
significant loss in sensitivity by age 60,
especially in the higher frequencies
Threshold values for males are poorer,
overall, than for females
Audiologic Characteristics
Associated with Aging
Recruitment



Abnormal growth of loudness
commonly associated with
damage to the cochlea
Due directly to the reduced
dynamic range
Makes the ear more sensitive
to loud sounds
Audiologic Characteristics
Associated with Aging
n
Speech Perception
n
Speech perception
suffers as we age, even if
we control for the change
in sensitivity associated
with aging