Speech audiometry
This test is performed to test the ability of the individual to hear and understand the spoken word. This has infact become the fundamental tool in hearing assessment. When performed with PTA it can aid in the determination of the degree and type of hearing loss. Information gained by speech audiometry can help in determination of proper gain and maximum output of hearing aids. It facilitates proper hearing aid prescription. It also facilitates audiological rehabilitation management.
Indications for speech audiometry:
1. Assessment of degree and type of hearing loss
2. Examination of word recognition abilities
3. Examination of discomfort / tolerance to speech stimuli
4. Determination of proper gain and maximum output of amplifying devices
Testing environment:
It is usually performed in a 2 room suite. Audiologist work from one room with the equipment while the patient will be seated in the other. The audiometric equipment room which will be occupied by the audiologist will contain the speech audiometer which is actually a part of the diagnostic audiometer. The speech testing portion of the diagnostic audiometer consists of two channels that provide various inputs and outputs.
Speech audiometer input devices:
This comprises of microphones for live voice testing, tape recorders and CD's for recorded testing.
Output devices:
This includes ear phones, ear inserts, bone conduction vibrators, loudspeakers. These are located in the testing room of the suite where the patient would be seated.
Speech tests can be performed using ear phones, with test material presented into one or both ear phones. Testing can also be performed using bone conduction vibrator. Sometimes speech material can be presented using loud speakers in the sound field environment.
Two parameters are tested:
1. Speech reception threshold
2. Discrimination score
Speech reception / speech awareness threshold measurement:
This parameter is also known as speech detection threshold. Basic objective of this measurement is to obtain the lowest level at which speech can be detected at least half the time. This does not involve the patient repeating the spoken word, but it requires the patient to merely indicate when the speech stimulus is heard. Words used for speech testing are usually spondaic. These words are two syllable words spoken with equal emphasis on each syllable (i.e. pan cake, hardware, playground). The advantages of spondees is that they are easily understandable and contain information within each syllable sufficient to allow reasonably accurate guessing. Measurement of speech reception threshold is useful in patients who are too young to understand spoken words. This test can also be used for patients who speak another language or who have impaired language function because of neurological deficit. In patients with normal hearing or somewhat flat hearing loss, this value is usually 10-15 dB better than the speech recognition threshold that requires patient to repeat the presented words. For patients with a sloping hearing loss, this measurment can be misleading with regard to indentifying the overall degree of the loss. If a patient has normal h earing in a low frequency range then speech awareness test will closely be related to the threshold for that frequency and it will not indicate greater loss in higher frequencies.
Speech recognition threshold:
This is also referred to as the speech reception threshold. The main objective of this testy is to obtain the lowest level at which speech can be identified and repeated at least half the time. Spondee words are used to perform this test. This test also helps in validation of pure tone thresholds as it has high correlation with it. In normal individuals the speech recognition threshold and three frequency average should be within 5-12 dB. This is true if hearing loss in the three measured frequencies are relatively similar. This test also establishes the sound level that needs to be presented for suprathreshold measures. It also helps in determining appropriate gain during hearing aid selection.
Suprathreshold word recognition testing:
The purpose of this test is to estimate the ability to understand and repeat single syllable words that are presented at conversational or another suprathreshold level. This test is also referred to as word discrimination or speech discrimination testing.
Word lists for this test are compiled for word recognition. These words are phonetically balanced. The original phonetically balanced word list was created at the Harvard Psycho acoustic laboratory and is referred to as the PB-50 lists. Generally presenting these words at 25-40 dB sensation level allows the patient to achieve maximum scores. Lowering the level results in lower scores.
This test helps in recognition of improvements achieved by persons with hearing aids. Testing the patient with hearing aid involves performing this test without the use of hearing aid and repeating the same after the patient wears the hearing aid. The score improvements can be used to provide the percent improvement score.
Special speech tests:
Sentense testing:
Also known as everyday sentense test. This test was first developed in 1950. Clinical use of this test however is rathe limited as its reliability is still not proved.
Synthetic sentence identification test:
This test was developed in the late 1960's. This test involves a set of 10 synthetic sentenses. 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. This test is not so challenging to the patient and hence it should be administered in noise at a signal to noise ratio of 0 dB, which means that the sentences are presented amidst noise at equal intensity level.
Speech perception in noise test:
This test was originally developed in 1970's. It went revision during the 1980"s. The revised test consists of 8 lists of 50 sentences. The last word of each sentence is considered to be the test item. Half of the 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 the sentence context. These recorded sentences come with a speech babble type noise that can be presentated at various signal to noise levels.
Speech in noise test:
This test was developed in 1990's. It contains 5 sentences with 5 keywords per test condition. Two signal levels i.e. 70 and 40 dB are used. About 4 speech to noise ratios are used at each level. A four talkier babble is used as noise. This recorded test can be given to patients with hearing aids in both the unaided and aided conditions.
Hearing in noise test:
The hearing in noise test is designed to measure speech recognition thresholds in both quiet and noise. This test consists of 25 lists of 10 sentences and noise matched to long term average speech. The 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.
Word in noise test:
This is also known as WIN test. It was developed in the early 2000's. This provides an open set of word recognition task without linguistic context. This test is composed of monosyllabic words presented in multitalker babble. The main purpose of this test is to determine the signal to babble ratio in decibels for those with normal and impaired hearing. This test is used to measure the performance of basic auditory function.
Most comfortable loudness level and uncomfortable loudness level:
The most comfortable loudness level determines the intensity level of speech that is most comfortably loud and is called the MCL test. For majority of normal hearing persons the speech is most comfortable at 40-50 dB above the speech reception threshold. This level is reduced for many patients with sensorineural hearing loss. This test can be used to determine the hearing aid gain for patients who need amplification.
The reason for uncomfortable loudness level test is to determine the upper limits of speech hearing. This level provides the maximum level at which word recognition tests can be administered.
Roll over phenomenon:
This phenomenon is seen in patients with retrocochlear hearing loss. These patients show a decrease in speech recognition as the intensity increases. The degree to which recognition decreases depends on the word list used.
