Speech Audiometry
Table of contents
- What is speech audiometry?
- Background
- Speech detection threshold (SDT)
- Speech recognition threshold (SRT)
- Word recognition (WR)
- Required equipment
- Speech setup
- Test procedure
- Speech results
- Speech in noise
- Binaural speech
- References
What is speech audiometry?
Basic speech audiometry uses speech signals to assess a person’s ability to hear speech, discriminate between words, and recall words. Advanced speech audiometry dives into the comprehension of speech.
Background
Many hearing aid users report trouble hearing speech, especially in noisy situations.
In this light, speech testing is a good tool to assess why the patient is troubled in certain hearing environments.
Speech audiometry employs speech signals and can be used to examine the processing ability and if it is affected by disorders of the middle ear, cochlea, auditory nerve, brainstem pathway, and auditory centers of the cortex.
More advanced speech testing considers how speech is understood in the presence of noise, such as:
- White noise
- Speech noise
- Babble noise
Using speech as the noise source can provide information on the signal-to-noise ratio (SNR) at which the patient can understand speech.
Other components such as the placement of the speech signal in relation to the noise source and the tonal differences between the speech signal and the masking signal are some of the things incorporated into advanced speech testing.
Speech detection threshold (SDT)
The speech detection threshold (SDT), also known as the speech reception threshold, is the level at which the patient can hear speech is present in 50% of the cases.
You can use the SDT as a cross-check of air conduction audiometry, which should closely agree with the pure‑tone average (PTA).
What is the pure-tone average (PTA)?
The PTA is the average of thresholds obtained at 500, 1000, and 2000 Hz.
For the PTA and SDT to ‘closely agree’, apply the following rules of thumb:
- ±6 dB or less = good
- ±7-12 dB = adequate
- ±13 dB or more = poor
Speech recognition threshold (SRT)
The speech recognition threshold (SRT) examines at which level the patient can repeat 50% of the speech material (usually numbers or spondaic words) correctly.
Also, the SRT gives an index of hearing sensitivity and helps to determine the starting point for other supra-threshold measures such as word recognition (WR).
Word recognition (WR)
WR, also known as speech discrimination (SD), is a score of the number of words correctly repeated, expressed as a percentage of correct (discrimination score) or incorrect (discrimination loss).
You can also score this as a phoneme score to know which phonemes the patient has difficulty hearing at a particular intensity level.
This is helpful for counseling and rehabilitation purposes.
Discrimination score / discrimination loss
You can either record this score in the Diagnostic Suite or with the audiometer keyboard on our standalone devices.
In the suite
Press the checkmark or the left arrow key to store a word as correctly repeated. Press the ‘X’ or the right arrow key to store a word as incorrectly repeated. Press the circle or ‘S’ on your keyboard to store the speech threshold in the speech graph (Figure 1).
Figure 1: Speech discrimination in the Diagnostic Suite.
On standalone devices
Press ‘Incorrect’ to store the word as incorrect or press ‘Correct’ to store the word as correct (Figure 2).
Figure 2: Speech discrimination with audiometer keyboard.
Phoneme score
When the speech material is indexed according to the number of phonemes in each word, the according soft key numbers will activate.
So, for a word with two phonemes, the soft keys ‘0’, ‘1’, and ‘2’ will be available to score.
When you score the word with the use of phonemes, the number of correct phonemes will appear below the word (Figure 3).
Figure 3: Words and their number of phonemes.
The phoneme score is calculated as a percentage: correct phonemes relative to total number of phonemes.
Required equipment
(1) Headphones, insert phones, or free field speakers
(2) A microphone, external sound player, or built-in wave files
(3) Talk back microphone and talk forward microphone
Speech setup
When running the speech test using wave files, you can present words in manual, continuous, or time out mode.
1. Manual mode
This allows you to manually press the tone switch/enter button to present the word and then score it as incorrect or correct before moving on to the next word.
2. Continuous mode
In this mode, the next word will automatically be presented after scoring incorrect or correct.
3. Time out mode
In this mode, the word played will be scored as either correct or incorrect if you do not enter the score within 1 to 5 seconds.
Test procedure
The procedure is outlined below step-by-step and is specific to our equipment.
Step 1
Before performing speech audiometry, you may wish to do the tone audiogram.
This provides valuable predictive information for speech testing, including information about when you need to apply masking.
Step 2
Press the ‘Tests’ button and select the ‘Speech’ test.
If needed, select the ‘Measurement type’ (WR1, WR2, WR3, SRT), ‘Type’ of measure (word, numbers, multi‑syllabic numbers, multi‑syllabic words), and ‘List’ of words using the soft buttons.
Select the intensity levels for channel 1. If you need to apply masking, configure channel 2 also.
Step 3
Explain to your patient that he/she will now hear some words/numbers/sentences though the earphones/free field speakers.
Instruct your patient to repeat what is said even though it may be very soft.
Encourage your patient to guess even if they are unsure about the word/number/sentence.
When performing the speech test in noise, instruct your patient to focus on the speech, not the noise.
Step 4
Press ‘Start’ to start presenting the words, numbers, or sentences.
Based on the settings for speech, you can score the response as ‘Correct’, ‘Incorrect’, or as the number of correct phonemes.
Step 5
Click on ‘Store’ to store the results.
Speech results
You can display the results in table mode or graph mode.
1. Table mode
Table mode allows for several SRTs using different test parameters, such as transducer type, test type, intensity, masking, and so forth (Figure 4).
Figure 4: Table mode.
2. Graph mode
When showing the SRT in graph mode, the speech audiogram calculates the SRT value, which is the distance in dB from the point where the normative curve crosses 50% to the point where the speech curve crosses 50% (Figure 5).
Figure 5: Graph mode.
The SRT value is how much you need to turn up the level compared to normal for the patient to be able to repeat 50%.
Use the m-curve for multi-syllabic words and the s-curve for single-syllabic words.
You can edit the curves according to the normative data you wish to use in the speech settings.
Note that the normative curves change based on the speech material.
Thus, you must ensure that WR1, WR2, or WR3 are linked to single- or multi-syllabic words to show the SRT.
Calculating the WR SRT is only available when using the suite.
Speech in noise
Problems understanding speech in noise is a common complaint from people with hearing loss.
Speech in noise testing provides useful information about the impact of the hearing loss on the patient’s ability to communicate.
It also provides information about whether the patient is getting the expected benefit from the hearing aids when communicating in noisy environments.
You can test the patient in a speech in noise environment using a free field setup to present the speech signal and noise signal from the same speaker or separate speakers.
Either present the signal and noise to the same ear with AC40 or select the speech in noise test with AD629.
Binaural speech
If you want to present the speech signal to both ears at the same time, select the same output for both channels with AC40.
With the AD629e, perform binaural speech by choosing the test ‘Speech-Ch2On’.
References
Stach, B.A (1998) Clinical Audiology: An Introduction, Cengage Learning.
