csd 5400 rehabilitation procedures for the hard of hearing

CSD 5400REHABILITATION

PROCEDURES FOR THE HARD OF HEARING

Auditory Perception of Speech and the Consequences of

Hearing Loss

Overview

The aural rehabilitation goal is to remediate the effects of a hearing impairmentUltimately comes down to

the effect of the hearing loss on speech recognition and perception

Develop a general understanding of what a hearing loss does to the speech signal

The Auditory System in Review

The primary purpose of the auditory system is to take the speech code at the periphery and convert it to a representation used by the CNS to extract meaning


Speech arrives to the auditory periphery as a series of pressure variations as a function of time

The normal auditory periphery converts these pressure variations into physical movement of the middle ear structures, which in turn causes fluid movement in the cochlea


Cochlear fluid movement gives rise to the traveling wave along the basilar membraneSpectral code

Depending on the site of maximum amplitude of displacement of the traveling wave, certain auditory nerves will be activatedNeural activityCritical band theorySpectral and temporal code


As the signal moves higher into the central pathways, more complicated processing occursBinaural processingTemporal processing

By the time the signal reaches the cortex, it has been analyzed and re-coded in a number of different ways

The cortex recognizes these various forms of analysis and extracts what is necessary, given the job at hand

When the Auditory System is Impaired

Speech is inaccurately coded at the peripheryDistortedMissingAttenuated

Loss of redundancyWhen the signal reaches

the cortex, the coded representation may be unrecognizable

Who’s Making Use of the Signal?

Important considerationAdults

Rely very heavily on the linguistic, contextual, and nonverbal cues available

ChildrenNo extensive language

base

Acoustic Cues of Speech

1. Frequency2. Intensity 3. Temporal

Characteristics

Flexer’s Analogy

Illustrating Hearing Loss

Tape examples

Acoustic Cues of Speech

Short Term Characteristics Long Term Characteristics

Long Term Characteristics of Speech

Average changes over relatively long periods of time

Provides general acoustic characteristics of speech

Long Term Characteristics of Speech

Mean intensity level of conversational speech is 65-70 dB SPL

Individual speech segments fluctuate around this mean by 40 dB

Long Term Speech Spectrum

Long-interval acoustic spectrum of male voices taken 17 inches from speaker’s lips

Maximum energy is at approximately 500 Hz Roll-off rate of 9 dB/octave

Phonemes

Smallest unit of speech to have linguistic meaning

Traditional unit of speech to study short term acoustic characteristics

Phonemes

Classification systemVowelsConsonants

Differences Between Vowels and Consonants

These two classes of sounds differ in the manner they are produced and in the way we perceive them Vowels are considered more “prime”

RhymingSpeech Errors

Vocal tract configuration Voicing

Short Term Acoustic Characteristics of Vowels

1. Vowels are always voiced

2. The vocal tract is relatively open

3. Source-Filter Theory of vowel production

Sound Source of Vowels

The glottal pulseThe lowest component is the

fundamental frequency (f0)

Harmonics are labeled Hx.

Maximum energy is at the fundamental frequency of the speaker

Above the fundamental frequency, the spectrum rolls off 10-12 dB/octave

Filter of Vowels

The vocal tract, which can be thought of as a tube open at one end, closed at the other, and of a specified length

Putting the Source and Filter Together

Putting the Source and Filter Together

n The panel at the left shows the glottal source. The panel at the right shows the spectrum of the source after filtering by a filter representing a neutral vocal tract. The spectral characteristics of the filter is indicated in the middle panel

Changing the Effects of the Filter

In order to produce these three different vowels, we change the characteristics of the vocal tract. This will alter the resonant frequency characteristics of the tube and change the combined spectrum of the glottal pulse and the vocal tract

Changing the Effects of the Source

n This is what happens when the same vowel is produced by a man, a woman and a child

An Important Short Term Acoustic Characteristic of

Vowels

Formants are the regions of increased spectral energy

They are only a characteristic of vowels The frequency regions they occupy, as well

as their relative intensities change as the vocal tract changes with each vowel production

All English vowels have 5-7 formants Vowels can be distinguished from one

another using the lowest (frequency) 2-3

Vocal Tract Shapes and Spectra

Vocal tract shapes and corresponding spectra (F1 and F2 only) for four back vowels

Vocal Tract Shapes and Spectra

n Vocal tract shapes and corresponding spectra (F1 and F2 only) for four front vowels

Peterson & Barney (1954)

Landmark spectrographic study of 76 men, women, and children producing vowels in isolation

Measured and reported the average fundamental frequency and the frequency/intensity of the first three formants of the ten English vowels

A Summary of Peterson & Barney’s Results

Articulation and the Formant Frequencies

F1 corresponds to the degree of tongue constriction in the vocal tract

F2 corresponds to how forward in the mouth the tongue is

F3 is not related in a simple way to articulatory parameters

Vowel Normalization

Vowel quadrilaterals for men, women, and children

What’s thought to be important for vowel perception is the relative spacing between F1 and F2; not their absolute frequencies

Consequences of Hearing Loss on Vowel Perception

Vowel perception is impaired when a hearing loss erodes the acoustic information in the F2 range

Generally 1000 Hz and aboveVowels are generally robust to the effects

of hearing loss

Short Term Acoustic Characteristics of Consonants

Differences Between Vowels and Consonants Consonants:

Have a shorter duration Can’t be isolated Don’t have just one noise source Aren’t static Identification seems to rely primarily on the vowel that

precedes or follows Have a variety of methods of production and places in the

vocal tract where they are produced

Spectral Regions of Various Speech Sounds

A common spectral representation of major speech sounds

Related to the threshold of audibility curve


Another exampleLines A, B, and C

represent three different configurations and degrees of hearing loss

What predictions can you make?


Intensity and frequency distribution of speech sounds overlaid on an audiogram

Predictions based on characteristics of the hearing loss

Predicting the Degree and Type of Phoneme Errors

These type of charts are used often to help predict the effect of a particular degree and configuration a hearing loss might have on speech understanding

This works somewhat, but it only looks at the influence of a hearing loss in terms of a filter

Sensorineural hearing loss is more complicated than thisAttenuation and distortion

Hearing Loss as a Loss of Redundancy

Illustrates the reduction of pattern details (redundancy)

The Consonant Classification System

n Every American English consonant can be identified uniquely according to its

1. Manner of articulation2. Place of articulation3. Voicing

Consonant Feature Classification System

n Classification of the consonants of American English according to the articulatory feature system

Acoustic Properties of Articulatory Features

Voicing:Energy is broadband

and extends from 100-4000 Hz


n Place of Articulationn Energy is very high

frequency and confined to 1000-8000 Hz


Manner of Articulation

Energy is spread through the mid frequencies (250-3500 Hz)

Consonants and Vowels Together

Schematic oral tract movements, etc for phrases a buy, a pie in the top spectrograms and a dye and a tie in the lower spectrograms

Formant Transitions

n Schematic of a transition and steady-state portion of a formant frequency

F2 Formant Transitions

The second formant transition provides a lot of information about the consonant

Place of articulation is related to the direction of the transition

Manner of articulation is related to the rate of the transition

Error Patterns with SNHL

Place of articulation and manner of articulation error rates for 38 SNHI listenersPlace of articulation

errors are more prevalent, followed by manner of articulation errors

Feature Recognition as a Function of Degree of HL

Auditory identification of temporal patterns of vowels and consonant features by 121 HI children as a function of PTANotice how place of artic

feature recognition is adversely affected by HL

Voicing and vowel id are better preserved

Summary of Findings…

General findings of studies of phoneme perception for SNHL when using meaningful CVC stimuliRelatively few errors are made with the vowel

When they do occur, they occur more often for front vowels

Higher F2 frequency

More errors are made with consonantsFinal position is extremely vulnerable

Most common error type is place of articulation, followed by manner of articulation

Voicing errors are rare

In Closing..

It appears that phoneme error types seem to relate somewhat to the frequency region and degree of hearing lossIf the hearing loss is primarily confined to the

high frequencies, then we tend to see more errors with articulatory features that are more high frequency weighted (e.g. place)

Our predictive ability stops here

In Closing..

In fact, we see tremendous variability among hard of hearing listeners in terms of their ability to perceive and understand speechThe amount and way information is coded varies

from listenerVarying degrees of distortion not related to the

characteristics of the audiogram

If information is restricted at the phonetic or spectral level, it is also probably restricted at the linguistic level

How well individuals are able to integrate information varies

csd 5400 rehabilitation procedures for the hard of hearing

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