CSD 2230INTRODUCTION 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 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

Intensities of Common Sounds

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

Characteristics of Normal Sound Perception and

Speech

Acoustic Cues of Speech

1. Frequency2. Intensity 3. 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 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?

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

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

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 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