Lecture 4- Speech Threshold Assessment Flashcards Preview

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Flashcards in Lecture 4- Speech Threshold Assessment Deck (19)
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1

What is the speech stimulus? How can the speech stimulus be represented on a speech spectrum?

Speech stimulus: a complex signal that varies in amplitude, duration, and frequency components

- On the spectrum, speech is composed of many frequencies
Peak: 500-700 Hz
Rolloff above 1000 Hz: 10-12 dB/octave

- There are similar spectrums for males, females, and different speakers

Relative intensity of speech components:
- Strongest components: vowels
- Weakest components: consonants

2

What is the LTASS?

Long-term average speech spectrum

- Most of the energy in speech is in the low frequencies due to the fundamental frequency from the voice and vowels

3

What is speech detectability?

Faintest level at which an individual can detect speech 50% of the time (SDT- speech detection threshold)

* Also known as the speech awareness threshold*

4

What is speech intelligibility?

Lowest intensity where the individual correctly repeats the material 50% of the time (SRT- speech reception threshold)

5

What is absolute intelligibility?

The faintest level at which the individual repeats 100% of the material

6

What are the relationships between the different speech thresholds?

- SDT is 8-9 dB < SRT, which is 4-5 dB less than the threshold of absolute intelligibility
- SDT = best threshold on audiogram (250-4000 Hz)
- SRT = average hearing in speech frequencies (500-2000 Hz)

7

Why do audiologists use speech thresholds?

1) To validate the pure tone audiogram
- Evaluate the relationship between sensitivity for speech and pure tones

2) Use as a reference intensity level
- Supra threshold speech recognition (dB SPL re: SRT)

3) Used to estimate hearing sensitivity
- For difficult to test patients

4) Used to determine hearing aid candidacy, estimate of benefits, monitor performance

8

What are some historical speech threshold tests?

1) Whispered speech tests
- Could occur in any doctor's office

2) Invention of phonograph (1877) - Edison
- Could present recorded material
- Intensity could be controlled

3) First speech audiometer (1926) - Bell Labs
- Presented phonographic recordings (digit pairs)
- Reduced intensity in 3-dB steps
- Measured articulation function for speech (% correct vs. presentation level)
- SRT corresponds to 50% point
- Developed Bell Telephone Intelligibility Lists (49 lists; 50 sentences)

4) Monitored Live voice testing (1942)
- Hughson & Thompson
- Hooked v-u meter to speech audiometer to monitor intensity of voice
- Measured SRT via pure-tone audiometric technique
- Noted a linear relationship between pure tone & speech threshold

5) CID (1950s) Hirsh - spondee disc recordings
- Stimuli: more familiar words than PAL
- Recordings: W1, constant level, W2, stair step

Tabular methods: start at suprathreshold level
- 3 words per step, in 3 dB steps
- Assign 1 dB for each correct word; count # of words correct
- Subtract # correct from starting level, add correction factor

Efforts to produce "homogeneous" list of spondees
- Threshold for different spondees obtained at similar levels
- Lists available with 15 selected spondees

9

What did the Harvard Psychoacoustics Labs (PAL) create?

Hudgins, et. al., 1947

- Developed materials for measuring SRT
- Criteria for selection of words used in test:
1- Highly audible and equally audible
2- Familiar vocabulary
3- Phonetic dissimilarity

84 words chosen = all spondees (= stress on 2 syllables)

- Recordings of spondee word lists
- Developed tabular form for measuring SRT

10

Describe the Tillman-Olsen Method for obtaining thresholds.

- A descending method with 2 phases

Preliminary phase
- Read words at 5 dB at supra threshold level, w/o visual cues
- Discard any words that the listener can't repeat
- Give the listener the instructions
- Present the words formally at supra threshold level
- Present 1 word, if correct, descend by 10 dB
- Continue until listener misses 2 words @ 1 level
- Increase level by 10 dB (this is the starting level)

Test Phase - record responses right or wrong
- Present 2 words per level
- Subject must repeat 1st 5/6 words correctly
- Descend in 2 dB steps
- Continue until listener misses last 5/6 words

Calculation of threshold?
T = starting level - # correct + 1 dB

11

What are the advantages & modifications of the Tillman- Olsen Method?

Advantages
- Standardized procedure
- Removes tested bias
- Highly reliable

Modifications
- Can use 5 dB steps, with 5 words on a step
- Correction factor = 2 dB

12

What is the current method for obtaining the SRT?

- Jahner, Schlauch, & Doyle (1994)

- Compared ASHA 1979 and T-O Methods for measuring SRT

Results:
- SRT with T-O method < 1979 method by 4 dB
- ASHA 1979 method agreed better with PTA and took less time to perform

Conclusions: for clinical purposes, two methods are similiar

13

What are variables that influence measurement of SRT?

- Descending vs. ascending method (not significant)
- Step size, 2 dB or 5 dB (not significant)
- Carrier phrase vs. no carrier phrase ( not significant)

Recorded vs. Monitored Live Voice
- MLV: widely used (flexible for kids/elderly)
- MLV: difficult to peak at 0 BU
- Results are reliable if they are the same tester
- To use standardized procedure- must use recorded material

Effect of prior knowledge of vocabulary and practice effects
- Improvement in SRT due to practice: 1 dB
- Improvement in SRT due to practice and possible prior knowledge (2.4 dB)
- Improvement in SRT due to prior knowledge of vocabulary (6 dB)
Conclusion: practice doesn't influence thresholds too much, but prior knowledge does
Recommend: familiarization of vocabulary

14

What is the relationship between speech and pure tone thresholds?

Comparison using SPL scale

Ex. SRT = 20 dB SPL
PTA = 11.5 + 7 + 9 dB SPL
= 9 dB SPL

Comparison using HL scale:
- Threshold for speech is approximately equal to the thresholds for pure tones

Acceptable agreement between PTA and SRT: +/- 6 dB --> +/- 12 dB

Reasons for lack of agreement

SRT

15

What are the methods for calculating pure tone average (PTA)?

Fletcher (1929) - 3 frequency PTA
-Average threshold for 500, 1000, and 2000 Hz, used for predictor of speech threshold

Carhart (1946)
- Correlation between PTA & SRT depends on audiogram configuration
- r = .79 (flat), r = .75 (gradually sloping), r = .29 (sharply sloping)
- Better SRT than PTA because speech is concentrated in low frequencies

Fletcher (1950): use average of best 2 thresholds in 500 to 2000 Hz range
- Works best when applied to sloping audiogram

- Use PTA or Fletcher average depending on slope of audiogram

16

When should someone use SDT?

- Use SDT when a person can't repeat spondees
- Examples: young children, individual with severe discrimination problems

Relationship between SDT and pure tone thresholds: agrees with best threshold on audiogram between 250 and 4000 Hz

17

How to obtain speech thresholds through bone conduction?

- Speech stimuli can be presented via bone conduction vibrator
- Useful for patients who don't respond well to pure tones (kids)
- Compare SRT via AC and BC (Air-bone gap)

Calibration of the bone oscillator for speech:
- Use listener's with normal hearing or sensorineural hearing loss
- Determine SRT via AC & adjust BC oscillator so that SRT via BC is the same

18

What are some modifications that can be made for children?

Special needs for children:
- Procedures for adults are OK with school-aged children
- Need to modify these techniques for younger children or multiply-handicapped kids because of:
- limited vocabulary
- limited expressive skills
- short attention span

Materials for a pediatric population:
- Use selected spondees within the child's vocabulary
- Published in ASHA. 1988 (ice cream, etc.)
- Use pictures or toys depicting spondees (for picture-pointing response)
- Helpful for kids w/ limited expressive skills
- Screen child before test

Methods
1) Picture Pointing
- Limit set to 12 or less (visual scan, memory load)
- Familiarize child with stimuli prior to test
- Use carrier phrases ("show me")
- Work in 5-dB steps, rather than 2-dB steps (faster)

2) Conditioning techniques: if limited vocabulary
- Use VRA
- Obtain MRL in SF - reflects hearing in better ear

3) Alerting response: if you can't condition child
- Use ascending method: note lowest level of response

19

Why is it important to establish SDT or SRT in children?

- Easier to establish than pure tone thresholds
- Indicates validity of pure tone thresholds
- Helps pick up children who are malingering