11-02-2013, 11:59 AM
SPEECH AUDIOMETRY
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Introduction
Speech audiometry is a test to find out hearing loss for speech; the levels required for their most comfortable levels and uncomfortable loudness level. It also tests the range of comfortable loudness and importantly, the ability to recognise the sounds of speech.
Instrumentation
The instrument used for speech audiometry is speech audiometer. It is usually built inside the pure tone audiometer.
The speech mode of the clinical audiometer includes the following components:
1. Various source of recorded speech materials, such as compact disk player or computer
2. A microphone for live wire testing
3. An input selector to choose the desired source of speech material.
4. An input level control which is used with VU meter to ensure speech signals are at the levels necessary for them to be properly calibrated. An attenuator to control the level of speech being presented to patient.
5. An output selector to direct the speech stimuli to desired output transducer
6. Output transducers.
7. Monitor earphone or loudspeaker to enable audiologist to hear the speech signals that are being presented to the patient
Test environment
Carried out with the patient isolated from examiner, this is mandatory when monitored voice testing is used because if examiner and patient are in same room there is no way to ensure that the patients are responding to sounds channelled to them through them through audiometer rather than directly through air in the room.
Recorded versus Monitored live voice
Recorded means words are spoken into a microphone by the audiologist who monitors her voice level on the audiometer’s VU meter.
Compared to monitored live voice testing, recorded materials provide much better control over the level and quality of the speech signals being presented to the patient.
Recorded voice has advantage of standardisation as well.
Live voice can be flexible according to different patients and can be modified according to individual needs.
Advantages of recorded material
• Provide consistency of presentation that is independent of expertise of the clinician.
• Standard material
• No subjective mistakes
• Takes less time
Patients role
Depending on the type of test : A response must be obtained in the form of oral reply, written reply, identification (pointing) of picture or object.
Oral response;
Advantage – good speed
Maintenance of rapport between patient and audiologist
Written responses;
Can be scored only on completion of the test, they eliminate errors caused by difficulties indiscriminating patients’ speech, provide permanent record of kinds of errors made, slow down the test process.
Pointing Pictures or objects;
Reserved for children who otherwise cannot participate in test, adults with special problem
Speech threshold testing
Speech threshold can be of two types; speech detection threshold and speech recognition threshold
Speech Detection threshold (SDT) maybe defined as the lowest level at which subject can barely detect the presence of speech and identify it as speech, 50% of the time is called speech detection threshold (Gelfand 1948). Sometimes called as Speech Awareness Threshold (SAT). Here the clinician presents any word/phrases/sentences as a speech material. Eg: hello, papapa, miew, mamama. He may also use a name call.
Speech recognition threshold;(SRT) defined as lowest hearing level at which speech signal is intelligible enough 50% of the time is speech recognition threshold.(ASHA 1979). It is measured as the intensity level in which the patient is repeating atleast half of the speech material given.
Variety of speech material is used for SRT;
• cold running speech a form of continues discourse maybe used to determine SRT by modifying instructions to the patient and altering response criteria
• Spondaic words are a word with two syllables both produced with equal stress and effort. These words both syllables should peak at zero at VU meter. On some pre-recorded spondee word list carrier phase precedes each word, eg “say the word”
Clinical functions of SRT:
1. To serve as measure for corroborating pure tone thresholds
2. To serve as reference point for deciding on appropriate levels at which at which to administered supra threshold speech recognition test
3. To determine hearing aid needs and performance
4. To ascertain the need for aural rehabilitation and progress in management
5. To determine hearing sensitivity for young children and those difficult to test.