Speech audiometry, in conjunction with pure-tone audiometry, can aid in determining the degree and type of hearing loss. Speech audiometry also provides information regarding discomfort or tolerance to speech stimuli and information on speech-discrimination abilities.
In addition, information gained by speech audiometry can help determine proper gain and maximum output of hearing aids and other amplifying devices for patients with significant hearing losses and help assess how well they hear in noise. Speech audiometry also facilitates audiological rehabilitation management.
In addition to pure-tone audiometry, speech audiometry provides information concerning sensitivity to speech materials and acuity or understanding of speech at suprathreshold levels.
Speech audiometry has become a fundamental tool in hearing-loss assessment. It can be used diagnostically to examine speech-processing abilities throughout the auditory system, and it can be used to crosscheck the validity of pure-tone thresholds.
In most circumstances, speech audiometry is performed in a 2-room testing suite. Audiologists work from the audiometric equipment room, while patients undergo testing in the evaluation room. The audiometric equipment room contains the speech audiometer, which is usually part of a diagnostic audiometer. The speech-testing portion of the diagnostic audiometer usually consists of 2 channels that provide various inputs and outputs.
Speech audiometer input devices include microphones (for live voice testing), tape recorders, and CDs for recorded testing. Various output devices, including earphones, ear inserts, bone-conduction vibrators, and loudspeakers, are located in the testing suite.
Tests using speech materials can be performed using earphones, with test material presented into 1 or both earphones. Testing can also be performed via a bone-conduction vibrator. In addition to these methods, speech material can be presented using loudspeakers in the sound-field environment.
Speech-awareness threshold (SAT) is also known as speech-detection threshold (SDT). The objective of this measurement is to obtain the lowest level at which speech can be detected at least half the time. This test does not have patients repeat words; it requires patients to merely indicate when speech stimuli are present.
Speech materials usually used to determine this measurement are spondees. Spondaic words are 2-syllable words spoken with equal emphasis on each syllable (eg, pancake, hardware, playground). Spondees are used because they are easily understandable and contain information within each syllable sufficient to allow reasonably accurate guessing.
The SAT is especially useful for patients too young to understand or repeat words. It may be the only behavioral measurement that can be made with this population. The SAT may also be used for patients who speak another language or who have impaired language function because of neurological insult.
For patients with normal hearing or somewhat flat hearing loss, this measure is usually 10-15 dB better than the speech-recognition threshold (SRT) that requires patients to repeat presented words. For patients with sloping hearing loss, this measurement can be misleading with regard to identifying the overall degree of loss.
If a patient has normal hearing in a low frequency, the SAT will be closely related to the threshold for that frequency, and it will not indicate greater loss in higher frequencies.
The speech-recognition threshold (SRT) is sometimes referred to as the speech-reception threshold. The objective of this measure is to obtain the lowest level at which speech can be identified at least half the time.
Spondees are usually used for this measurement. Lists of spondaic words commonly used to obtain the SRT are contained within the Central Institute for the Deaf (CID) Auditory List W-1 and W-2.
In addition to determining softest levels at which patients can hear and repeat words, the SRT is also used to validate pure-tone thresholds because of high correlation between the SRT and the average of pure-tone thresholds at 500, 1000, and 2000 Hz.
In clinical practice, the SRT and 3-frequency average should be within 6 dB. This correlation holds true if hearing loss in the 3 measured frequencies is relatively similar. If 1 threshold within the 3 frequencies is significantly higher than the others, the SRT will usually be considerably better than the 3-frequency average.
Other clinical uses of the SRT include establishing the sound level to present suprathreshold measures and determining appropriate gain during hearing aid selection.
Suprathreshold Word-Recognition Testing
The primary purpose of suprathreshold word-recognition testing is to estimate ability to understand and repeat single-syllable words presented at conversational or another suprathreshold level. This type of testing is also referred to as word-discrimination testing or speech-discrimination testing.
Initial word lists compiled for word-recognition testing were phonetically balanced (PB). This term indicated that phonetic composition of the lists was equivalent and representative of connected English discourse.
The original PB lists were created at the Harvard Psycho-Acoustic Laboratory and are referred to as the PB-50 lists. The PB-50 lists contain 50 single-syllable words in 20 lists consisting of 1000 different monosyllabic words. Several years later, the CID W-22 word lists were devised, primarily using words selected from the PB-50 lists. Another word list (devised from a grouping of 200 consonant-nucleus-consonant [CNC] words) is called the Northwestern University Test No. 6 (NU-6). Recorded tape and CD versions of all these word-recognition tests are commercially available.
The PB-50, CID W-22, and NU-6 word lists each contain 50 words that are presented at specified sensation levels. Words can be presented via tape, CD, or monitored live voice. Patients are asked to repeat words to the audiologist. Each word repeated correctly is valued at 2%, and scores are tallied as a percent-correct value.
Varying the presentation level of monosyllabic words reveals a variety of performance-intensity functions for these word lists. In general, presenting words at 25-40 dB sensation level (refer to the SRT) allows patients to achieve maximum scores. Lowering the level results in lower scores. For individuals with hearing loss, words can be presented at a comfortable loudness level or at the highest reasonable level before discomfort occurs.
When words are presented at the highest reasonable level and the word-recognition score is 80% or better, testing can be discontinued. If the score is lower than 80%, further testing at lower presentation levels is recommended. If scores at lower levels are better than those obtained at higher presentation levels, “roll over” has occurred, and these scores indicate a possible retrocochlear (or higher) site of lesion.
Another use of suprathreshold word-recognition testing is to verify speech-recognition improvements achieved by persons with hearing aids. Testing can be completed at conversational levels in the sound field without the use of hearing aids and then again with hearing aids fitted to the patient. Score differences can be used as a method to assess hearing with hearing aids and can be used as a pretest and posttest to provide a percent-improvement score.
To evaluate ability to hear and understand everyday speech, various tests have been developed that use sentences as test items. Sentences can provide information regarding the time domain of everyday speech and can approximate contextual characteristics of conversational speech.
Everyday sentence test
This is the first sentence test developed at the CID in the 1950s. Clinical use of this test is limited, because its reliability as a speech-recognition test for sentences remains undemonstrated.
Synthetic-sentence identification test
The synthetic-sentence identification (SSI) test was developed in the late 1960s. SSI involves a set of 10 synthetic sentences. Sentences used in this test were constructed so that each successive group of 3 words in a sentence is itself meaningful but the entire sentence is not.
Because the sentences are deemed insufficiently challenging in quiet environments, a recommendation has been made that sentences be administered in noise at a signal-to-noise (S/N) ratio of 0 dB, which presents both sentences and noise at equal intensity level.
Speech perception in noise test
The speech perception in noise (SPIN) test is another sentence-identification test. The SPIN test was originally developed in the late 1970s and was revised in the mid 1980s.
The revised SPIN test consists of 8 lists of 50 sentences. The last word of each sentence is considered the test item. Half of listed sentences contain test items classified as having high predictability, indicating that the word is very predictable given the sentence context. The other half of listed sentences contain test items classified as having low predictability, indicating that the word is not predictable given sentence context. Recorded sentences come with a speech babble-type noise that can be presented at various S/N ratios.
Speech in noise test
The speech in noise (SIN) test, developed in the late 1990s, contains 5 sentences with 5 key words per test condition. Two signal levels (70 and 40 dB) and 4 S/N ratios are used at each level. A 4-talker babble is used as noise. This recorded test can be given to patients with hearing aids in both the unaided and aided conditions. Results are presented as performance-intensity functions in noise. A shorter version of the SIN, the QuickSin, was developed in 2004.
Hearing in noise test
The hearing in noise test (HINT) is designed to measure speech recognition thresholds in both quiet and noise. The test consists of 25 lists of 10 sentences and noise matched to long-term average speech. Using an adaptive procedure, a reception threshold for sentences is obtained while noise is presented at a constant level. Results can be compared with normative data to determine the patient’s relative ability to hear in noise.
Most Comfortable Loudness Level and Uncomfortable Loudness Level
Most comfortable loudness level
The test that determines the intensity level of speech that is most comfortably loud is called the most comfortable loudness level (MCL) test.
For most patients with normal hearing, speech is most comfortable at 40-50 dB above SRT. This sensation level is reduced for many patients who have sensorineural hearing loss (SNHL). Because of this variation, MCL can be used to help determine hearing aid gain for patients who are candidates for amplification.
MCL measurement can be obtained using cold running or continuous speech via recorded or monitored live-voice presentation. Patients are instructed to indicate when speech is perceived to be at the MCL. Initial speech levels may be presented at slightly above SRT and then progressively increased until MCL is achieved. Once MCL is achieved, a speech level is presented above initial MCL and reduced until another MCL is obtained. This bracketing technique provides average MCL.
Uncomfortable loudness level
One reason to establish uncomfortable loudness level (UCL) is to determine the upper hearing limit for speech. This level provides the maximum level at which word-recognition tests can be administered. UCL can also indicate maximum tolerable amplification.
Another reason to establish UCL is to determine the dynamic speech range. Dynamic range represents the limits of useful hearing in each ear and is computed by subtracting SRT from UCL. For many patients with SNHL, this range can be extremely limited because of recruitment.
UCL speech materials can be the same as for MCL. The normal ear should be able to accept hearing levels of 90-100 dB. Instruct patients to indicate when presented speech is uncomfortably loud. Instructions are critical, since patients must allow speech above MCL before indicating discomfort.
Pediatric Speech Materials
For very young children with limited expressive and receptive language skills, picture cards representing spondaic words can be used to establish SRT. Before testing, the tester must ensure that the child understands what the card represents. Once the child has been taught to point to the correct picture card, 4-6 cards are chosen and presented to the child. Then, the softest level at which the child can select the correct card at least half the time is established.
For children with typical kindergarten or first-grade language skills, the Children’s Spondee Word List can be used instead of adult word lists. The CID W-1 list is appropriate for use with older children.
Word-recognition testing for children can be classified as open-message response testing or closed-response testing. Closed-response testing uses the picture-pointing technique.
Word intelligibility by picture identification test
One of the more popular closed-response tests is the word intelligibility by picture identification (WIPI) test. This test consists of 25 pages; on each page are 6 colored pictures representing an item named by a monosyllabic word. Four pictures represent a test item, while the other 2 serve to decrease probability of a correct guess. WIPI was developed for use with children with hearing impairment and can be used for children aged 4 years and older.
Northwestern University children’s perception of speech test
Another popular closed-response test is the Northwestern University children’s perception of speech (NU-CHIPS) test. NU-CHIPS consists of 50 pages with 4 pictures per page and was developed for use with children aged 3 years and older.
Pediatric speech intelligibility test
The pediatric speech intelligibility (PSI) test uses both monosyllabic words and sentence test items. The PSI test consists of 20 monosyllabic words and 10 sentences. Children point to the appropriate picture representing the word or sentence presented. Test materials are applicable for children aged as young as 3 years.
Phonetically balanced kindergarten test
One of the more popular open-message response tests for children is the phonetically balanced kindergarten (PBK) test, which contains 50 monosyllabic words that the child repeats. The PKB test is most appropriate for children aged 5-7 years.
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