Transcript Speech Detection Threshold

Speech Audiometry
SPA 4302
Summer A, 2004
The Diagnostic Audiometer
Equipped with
• Inputs for microphones, cassette tapes, or CDs
• Volume unit (VU) meters
• Circuit for masking noise or mixing noise with
speech in the same ear
• Ability to test monaurally or binaurally
• Intensity levels ranging from -10 to 110 dB HL
• Outputs for auxilliary amplifiers (to speakers)
• Talkback system to allow patient/clinician
communication from different rooms/booths
The Patient’s Role in Speech
Audiometry
• Pt must know and be able to respond to
word in the language of the test.
• Responses:
–
–
–
–
Verbal repetition
Writing or marking response
Picture pointing
Clicking on choice on computer
The Clinician’s Role in Speech
Audiometry
• Must be able to convey to pt their task,
• Keep face from pt’s view
• Understand pt responses
Speech-Threshold Testing
• Speech Detection Threshold: lowest level at
which the listener can tell that something is there
(when the signal happens to be speech). Also
called the speech awareness threshold.
• Speech Recognition Threshold: lowest level at
which the listener can actual identify what the
speech stimulus is. Also called the Spondee
threshold.
SRT Stimuli: Spondees
• 2-syllable words with equal stress
• can be divided into two monosyllables
• e.g., hotdog, baseball, whitewash,
mousetrap, birthday, eardrum...
Why spondees?
• because their intelligibility curves rise from
near chance to 100% performance within a
few decibels. (see curve 1 in figure 5.1)
• This provides a much more accurate
threshold.
SRT Methods
•
•
•
•
•
Descending Approach
Start approx 10 dB above
expected threshold
Drop in 5 dB steps
5 words per level
Stop when pt misses 5 out
of last 6 words
Threshold = start level –
number correct +
correction factor
Adaptive Approach
• Like Pure Tone procedure
down in 10 dB steps, up in
5 dB steps
• Up to 4 words per level
• Threshold = lowest level
at which pt correctly id’s
at least 2 words (>50%).
Masking for SRT
• If SRT - IA > best BC Thresh NTE
• Put in at least:
STARTING LEVEL=SRTTE –35 +ABGNTE
But no more than:
OVERMASK = EMNTE-IA> Best BC Thresh
TE
Most Comfortable Loudness Level
• Instructions important: you can strongly influence
how a person responds.
• "I am going to continue talking to you as I make
my voice louder and softer. I will keep asking you
to tell me whether my voice is too soft, too loud or
comfortably loud."
• Do a number of sweeps in level.
• normally between 40 and 55 dB above SRT
Uncomfortable Loudness Level
• Begin at MCL, raise level as you continue to talk.
• "I am now going to ask you to tell me how my
voice sounds to you as I make it louder. Please
tell me if the level is comfortable, a little loud, or
uncomfortably loud.”
• Uncomfortable = loud enough so you would not
want to listen to my voice for a long time.
Range of Comfortable Loudness
•
•
•
•
•
(Or the Dynamic Range for Speech)
= UCL – SRT
Normally 100 dB or greater
Unchanged in conductive losses
Can be much smaller in sensorineural
hearing loss
Word Recognition Testing
• Open set-client can respond with any word he/she
can think of.
• Closed set-response options are provided for the
client (multiple choice test).
• Free response-client is free to respond or not.
• Forced Response-client must say something.
•
• [Forced choice = closed set forced response.]
Phonetically Balanced Word Lists
• selection of a group of words so that each
phoneme appears with the same frequency
it has in the normal lexicon. Based on
Thorndike-Lorge lists of words and word
frequencies.
• So-called PB word lists-- CID W-22 Lists
• Four lists of 50 words each.
CNC Word Lists
• Consonant-Nucleus-Consonant words
• Phonemically balanced
• Four 50-item lists: the NU-6 Word Lists
Alternative Speech Choices
• High Frequency Word Lists
– Gardner’s Hi Frequency Word Lists
– California Consonant Test
• Nonsense Syllable Lists
– The Nonsense Syllable Test (NST)
• Sentence Tests
– The Synthetic Sentence Identification (SSI) test
– Speech Perception in Noise (SPIN) test
– Connected Speech Test (CST)
Children’s Tests
• Word Intelligibility by Picture Identification
(WIPI) test – six pictures to choose from.
• Northwestern University Children’s Perception
of Speech (NUCHIPS) test – four pictures to
choose from
• Monosyllable-Spondee-Trochee test –
distinguishing word shapes, not identifying
particular words; used in cochlear implant
cases.
100
Performance-Intensity
Functions
90
80
% Correct
• PI70function: word recognition scores obtained
at60a range of stimulus levels.
NORMAL
50
• Curve
reaches a peak (Pbmax), and then ROLLOVER
40
• Either
remains high (normal), or
30
• Drops at higher levels (Rollover)
20
10
• Rollover
Index = (PBmax – Pbmin)/PBmax
0
20
40
60
70
dB HL
80
90
Rollover Indices for the preceding
examples
• Normal: (100 - 100) / 100 = 0.0
• Rollover: (44 - 20) / 44 = 0.54
• Rollover Indices of 0.45 or greater indicate a
neural (VIIIth nerve) problem.
Cross Hearing & the Need to Mask
• If Word level (HL)TE – IA > Best BCNTE
• Use Pink (Speech) Noise, or white noise
• EM = PBHL TE – IA + ABGNTE
Interpreting Word Recognition Scores
Score:
General Word Recognition Ability:
90 to 100
Within Normal Limits
75 to 90
Slight Difficulty
60 to 75
Moderate Difficulty
50 to 60
Poor
< 50
Very poor
Predicting WRS from the audiogram:
The AI
• The Articulation Index
• Audibility Index
• “Count the dot” audiogram
• If word recognition is poorer than prediction:
think neural hearing loss or central disorder.