An investigation into the effect of limiting the frequency bandwidth of speech on speech recognition in adult cochlear implant users

The purpose of this study was to investigate the effect of the limited-frequency bandwidth employed by telephones (300-3400 Hz) on speech recognition in adult cochlear implant users. The Four Alternative Auditory Feature (FAAF) test was used in four conditions: unfiltered and in three filtered conditions of 300-4500 Hz, 300-3400 Hz and 300-2500 Hz. Ten subjects implanted with the Nucleus CI24M device and 10 normal-hearing listeners were assessed to examine differences between word discrimination scores in each condition. Scores obtained from the 300-3400-Hz and 300-2500-Hz filtered conditions were significantly worse than those with unfiltered speech for the cochlear implant subjects, decreasing by 17.7% and 21.4%, respectively, from scores with unfiltered speech. By contrast, the normal-hearing listeners did not experience difficulties in discriminating between words in any of the conditions. Analysis of the word errors demonstrated that the reduction in implant subject scores with bandwidth arose from errors in place of articulation. Filtering speech in this way has a significant effect on speech recognition for cochlear implant subjects but not normal-hearing listeners. Hence, the limitations of the normal telephone bandwidth can be expected to have a negative effect on speech recognition for cochlear implant users using the telephone. Sumario El objetivo de este estudio fue investigar los efectos de la banda de frecuencia limitada que utilizan los tele´fonos (300-3400 Hz) en el reconocimiento del lenguaje en adultos con implante coclear. Se utilizo´ la prueba de cuatro caracteri´sticas auditivas alternativas (FAAF) en cuatro diferentes condiciones: sin filtro y con tres modalidades de filtracio´n: 300-4500 Hz, 300-3400 Hz y 300-2500 Hz. Se evaluaron diez sujetos implantados con el Nucleus C124M y 10 sujetos normales para conocer las diferencias en la puntuacio´n de discriminacio´n de la palabra en cada condicio´n. La puntuacio´n obtenida de la filtracio´n a 300-3400 Hz y a 300-2500 Hz fueron significativamente peores que aquellas sin filtracio´n en los sujetos implantados, con un decremento del 17.7% y 21.4% respectivamente a partir de la puntuacio´n de la condicio´n sin filtro. En contraste, los sujetos normales no mostraron dificultades en la discriminacio´n de palabras en ninguna de las condiciones. El ana´lisis de los errores cometidos demostro´ que la reduccio´n de las puntuaciones en los sujetos implantados fue en el punto de articulacio´n. Esta filtracio´n del lenguaje tiene un efecto significativo en el reconocimiento del lenguaje en los sujetos con implante coclear, pero no asi´ en los sujetos con audicio´n normal. Por lo tanto, es de esperar que la limitacio´n del ancho de banda de los tele´fonos tenga un efecto negativo en el reconocimiento del lenguaje en los implantados que utilizan el tele´fono.

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