Using Carrier Phrases to Assess Hearing Aid Performance
Versfeld and Goverts (2013) report that the functional benefit of hearing aids is often evaluated through presentation of single words (most often monosyllabic). However, hearing aid performance is impacted by the quality and quantity of signal-processing techniques employed within the hearing aid. Of note, words presented in isolation trigger different processing strategies and protocols (within a given hearing aid) than would natural conversational situations.
Versfeld and Goverts state that "hearing aid parameter settings depend on the incoming signal" and the preceding acoustic events impact the applied processing. Specifically, slow attack times (with regard to amplitude compression) can vary the output of the hearing aid. For example, when silent periods occur prior to monosyllabic word presentation, the hearing aid’s amplitude compression algorithm (and other automatic functions) increases gain (and alters other parameters) during the silent period and decreases gain (and alters other parameters) as the stimuli is presented. Therefore, multiple factors facilitate changes in the processing as the stimuli are processed. Words presented in quiet and in isolation may yield a different hearing aid output from words presented in natural speech patterns (in quiet and/or noisy environments) and/or monosyllabic words presented with a carrier phrase (such as "say the word").
The authors presented single words in isolation and single words presented following a carrier phrase at 50, 65 and 80 dBA loudness levels across ten hearing aid conditions, through seven hearing aids (from five manufacturers). Hearing aids were programmed to the manufacturer’s first fit, as prescribed for a flat 60 dB sensorineural hearing loss.
The authors note that in the final conclusion, adding a carrier phrase did not change the hearing aid output for the majority of hearing aids tested. However, for some hearing aids, the addition of the carrier phrase varied the output by some 3.5 dB, which could represent a 25-50 percent change in word recognition scores. The authors recommend carrier phrases should be used when evaluating hearing aids.
For More Information, References, and Recommendations
Versfeld NJ, Goverts ST. (2013) The Effect of a Carrier Phrase on Hearing Aid Amplification of Single Words in Quiet. International Journal of Audiology 52:189-193.