Audiometry, the measurement of hearing, is most commonly done using pure tones generated by a machine called an audiometer. With pure tone audiometry, precisely controlled auditory signals are used to elicit a response so as to establish the listener’s threshold of hearing ability. It provides valuable information about a person’s hearing sensitivity, type and degree of hearing loss, if any, but it does not give any clue as to their ability to hear and understand speech in different environments, or how it affects communication for them. This is where speech audiology comes in.
Speech testing also is performed using an audiometer, but instead of producing pure tones, a speech mode setting is used on the instrument which produces recorded speech to the listener. Live speech captured with a microphone and routed through a VU meter can also be used. A variety of speech audiometric tests are available, with recorded speech materials being preferred for their consistency and ability to be calibrated.
There are a few different types of test, including Speech Regognition Threshold (SRT), Sppech Detection Threshold (SDT), and Suprathreshold Audiometry.
The best words used for these tests have been determined through extensive research to be two syllable compound words that have equal stress on each syllable, called spondees. Examples of spondees would be Houseboat, Airport, Outside, etc. In SRT testing, words are presented to the testee at varying intensity levels starting from soft to loud, until the testee gives a response, and is then able to correctly identify the words, either by repeating it, writing it down, or picking it out from a written list. The lowest intensity level at which they respond to 50% of the words is in this manner established their speech recognition threshold.
In contrast, the speech detection threshold (SDT) establishes the lowest intensity level at which the listener can detect that speech stimuli is present, regardless of whether they understand it or not. It is useful to know the level of awareness of speech in cases where the SRT test may not be possible, for example in infants or when neurological damage to speech recognition centers has occurred.