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CSD 2230INTRODUCTION TO HUMAN
COMMUNICATION DISORDERS
Normal Sound Perception, Speech Perception, and Auditory
Characteristics at the Boundaries of the Lifespan
PowerPoint Access
You may access this presentation through my website:
http://www.d.umn.edu/~floven/
Just click on the CSD 2230 link on my home page.
The Perception of Sound
Psychoacoustics is a branch of experimental psychology interested in these questions
Overview of Perceptionn Although the physical
characteristics used to measure sounds are objective, how we experience sounds is subjective
Objective Characteristics• Intensity • Frequency• Duration
Subjective CharacteristicsPitchLoudness
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 SensitivityNormal 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 rangeBest sensitivity is
between 1000-5000 HzAs 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
Thresholds Absolute sensitivity--the minimum
intensity at which a listener can distinguish sound from silence
üDetection
Differential sensitivity--the smallest change in a stimulus a listener is just able to detect
nDiscrimination
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
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 Non-Categorically
n 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
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 consonantvoice 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?
OrDo we eventually learn to perceive
speech categorically?
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
n Reflexes observed when loud sounds are presented to an infant:
n The startle response
n The auropalpebral response
Attentive Behaviors in Newborns and Infants
n Quieting responsesn Increase in ongoing
activitiesn Changes in breathing
raten Changes in
vocalizationn Eye widening and
searchingn 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
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 oldStimuli 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 ageStimuli included phonemic contrasts from Salish and Hindi
languagesResponses included a non-nutritive sucking responseResults suggested that the younger infants listening to
the non-native 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 non-native 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 Acuity:n Changes in pure
tone sensitivity (absolute thresholds) among older adults emerges gradually as age increases.
Changes in Detection as a Function of Age and Gendern Two trends are clear from these
data:1) Both males and females exhibit a
significant loss in sensitivity by age 60, especially in the higher frequencies
2) 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