Lecture 5 - Supra threshold Speech Recognition I Flashcards Preview

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Flashcards in Lecture 5 - Supra threshold Speech Recognition I Deck (19):
1

What are the purposes of speech recognition testing?

1) Assess precision of speech transmission system
2) Access precision of individual's speech reception
- Assumes an ideal transmission system
- Clinical implications: diagnostic purposes, estimating functional deficits of hearing loss
3) Both purposes incorporate understanding of speech
- Using supra threshold presentation to determine how well an individual performs

2

What are the requirements of a speech recognition test?

1) Material should be representative of the language
- Concept of validity: performance should reflect the person's ability to understand every day speech
- Use material that represents the language
- Test materials developed to reflect the sounds in average speech

2) Test results should be reliable (repeatable)

3) Test should be easy to score

4) Materials should be relatively difficult to obtain a measure of the person's speech intelligibility problem
- Nonsense Syllables: too abstract, too difficult for some people; measures absolute recognizability rather than intelligibility
- Monosyllabic words: not abstract, not too much redundancy, a measure of intelligibility
- Multisyllabic words: scores are influenced by knowledge of the language (lexicon)
- Sentences: knowledge of syntax, semantics, and linguistic affects performance

3

What is the history of monosyllabic word tests (Harvard PAL)?

1st attempt to develop a test of speech recognition
- Called Harvard PAL PB-50s

Purpose for test development: assess communication
- System or individual

First requirement: wanted a valid test
- Phonetic balancing scheme: individual phonemes occur as frequently on the list as they do in the language
- Based on published data of phonetic composition of 100,000 words

Second Requirement: monosyllabic in structure
- Measure individual's ability to discriminate among fine elemetns of speech (multisyllabic words - too easy, nonsense syllables - too difficult)

Third requirement: lists of equal difficulty
- Concept of list equivalence
- Range of difficulty on each list

Fourth requirement: words should be in common usage

4

Describe the Harvard PAL PB50 monosyllabic word test.

- 20 lists, 50 words/list
- Never recorded at Harbard
- Later recording (very difficult test)
- Most widely used as MLV
- Carrier phrase: "Say the word...."
- Peak a word in carrier phrase at 0 VU

5

Describe the CID W-22 PB

Criteria:
- Monosyllables
- Highly familiar words
- Phonetic balance: based on printed and spoken English

Developed 4 lists, 50 words each
- Recordings with Hirsh as speaker
- List 1 was easier than Lists 2, 3, 4
- High test-retest reliability

6

Describe a psychometric functions.

- X axis is presentation level in dB SPL
- Y axis is the percentage of correct score
- Linear segment: steady or fixed increase in speech recognition score
- We're interested in what level the listeners score 100%
- We're interested in the linear segment
- PB Max: where the person reaches their maximum score on a speech recognition test
- Increases 5% per dB (steep rise)

7

How do the psychometric functions of different speech tests differ?

CID W-22
- Steeper slope

PAL PB 50s
- Has a gradual (shallow) slope (3-4% per dB)

8

What is the NU-6?

Northwestern University Test No. 6 (NU6)
- Tillman & Carhart, 1966

Goal for test development: list equivalence

Scheme of phonemic balancing
- Based on frequency of occurrence of phonemes within their set of words, not on English

Developed 4 lists; 50 words/list
- Recordings made (male & female talkers)
- Highly common monosyllabic words
- Looked at the frquency occurrence of each phoneme as it appears on the original list of words

- New recordings on CD made by VA with female talker

9

What is the psychometric function of the NU-6?

Normal hearing and conductive hearing losses
- Slope: 6% dB, 100% score at 24 dB SL re: SRT

People with sensorineural hearing loss
- Slope: 3.5%; plateau at 40 dB SL re: SRT
- Mean plateau was 92% correct

- Good inter-list equivalence

10

What are the effects of MLV vs. recorded materials on performance on PB wordlists?

1) MLV vs. Recorded Materials
Advantages of recorded materials
- Easier to administer (words peaking correctly)
- Standardized - can compare results between clincs
- More reliable

Advantages of MLV
- More flexible presentation
- Faster

Disadvantages of MLV - talker differences

- ASHA recommendations - recorded preferred
- Research findings - inconsistent

11

What is the performance-intensity function (PIF)?

- Only way to be sure that you're measuring PB-max
- Limitations: takes time
- Compromise: estimate level needed for PB-max

12

What are the effects of presentation level on performance on PB word lists?

Presentation Level
Goal: often want to measure best performance

Procedures that are not recommended:
- MCL does not equal the level needed for PB-max
- Fixed presentation (sensation) level above SRT

Procedures that are recommended:
- Fixed SPL (95 dB SPL)
- Just below LDL
- Adaptive procedure to estimate level

13

What are the effects of word familiarity on performance on PB word lists?

Word Familiarity
- Individual's lack of familiarity will affect some

14

What are the effects of half vs. whole lists on performance on the PB word lists?

Half vs. whole lists

Advantages of half lists
- Shorter test time
- May be sufficient for diagnostic purposes
- High intra-list reliability (1/2 list to whole list)

Disadvantages of half lists
- Sacrifice phonetic balance (lose face validity)
- Sacrifice inter-list equivalence
- Lower reliability than full lists

Decision based on purpose of testing
- Estimating everyday performance --> full list
- Diagnostic purposes --> half lists may be OK

15

What is the binomial probability theorem and how does it relate to clinical testing?

- The theorem shows that the standard deviation is inversely proportional to the square root of the number of test items (N)

Implications
- As N increases, standard deviation decreases
(results are more reliable with longer lists)
- As percent correct score varies:
Scores near 0 and 100% are more reliable
Scores near 50% are least reliable

Implications for clinical testing:
- Use longer lists when possible
- Use tables to indicate standard deviation of a given score to determine if a second score is significantly different from the first score

16

What is better for speech threshold testing: word or phonemic scoring?

- More precision is obtained with phonemic scoring
- Scores on half lists had higher variability than on full lists
- Phoneme scores were higher than word scores fro same condition
- Standard deviations were smaller for phoneme scoring than word scoring
- WRSs based on full lists analyzed by percentage of phonemes correct was the most effective test for improving precision of word rec. tests

17

What is the lexical neighborhood test?

- Developing for hearing impaired kids using sensory aids
- Limitation of PB-L: vocabulary too difficult

Test development
- Vocabulary items: taken from children's speech (3-5 years)
- Lexical difficulty: half of the words are lexically easy and half are lexically hard

Lexical neighborhood: all of the words that vary by one phoneme compared to the given word (ex. pit: lexical neighborhood include bit, sit, etc.)

LNT: 50-item lists of monosyllabic words
MLNT (multi-syllabic lexical neighborhood test): 50-item lists of 2 or 3-syllable words

Conclusion: LNT and MLNT should yield estimates of spoken word recognition in kids

18

What are lexically easy and lexically hard words?

Lexically easy: used with high frequency and come from sparse lexical neighborhoods (ex. juice)

Lexically hard: not used often and come from dense lexical neighborhoods (ex. thumb, pie, wet)

19

What is the neighborhood activation model and its effets on speech recognition performance?

Dirks et al. study (2001)

- Examined effects of word frequency, word density, and neighborhood frequency on word recognition performance in hearing impaired adults

Word frequency: frequency of occurence of word in language

Word density #: # of phonetically similar words

Neighborhood frequency: frequency of occurrence of phonetically similar words

For normal and hearing impaired adults
- High frequency words > low frequency words
- Words in low density neighborhoods > words in high density neighborhoods
- Words in low frequency neighborhoods > words in high frequency neighborhoods

Conclusion: speech recognition tests should take into account the cognitive-lexical principles of NAM