Limiares de reconhecimento de sentenças em indivíduos normo-ouvintes na presença de ruído incidente de diferentes ângulos  <span class="so-article-trans-title" dir="auto"> Translated title: Sentences recognition thresholds in normal hearing individuals in the presence of inciding noise from different angles </span>

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Abstract

OBJETIVO: Determinar e comparar os limiares de reconhecimento de sentenças no ruído, em campo livre, na presença de ruído incidente de diferentes ângulos e verificar qual a condição de escuta mais desfavorável, em indivíduos normo-ouvintes. MÉTODOS: Aplicou-se o teste Listas de Sentenças em Português em 38 adultos jovens, avaliados em cabine acústica. As sentenças foram apresentadas a 0°- 0º azimute e o ruído competitivo a 0°- 0°, 0º- 90º, 0º - 180° e 0º - 270º azimute, em intensidade fixa de 65 dB NPS (A). RESULTADOS: As relações sinal-ruído nas quais foram obtidos os limiares de reconhecimento de sentenças no ruído para estes ângulos de incidência foram, respectivamente: -7,56, -11,11, -9,75 e -10,43 dB. Houve diferença entre os resultados nas condições: 0º- 0º e 0º - 90º; 0º - 0º e 0º - 180º; - 0º - 0º e 0º - 270º. CONCLUSÃO: Os seguintes limiares de reconhecimento de sentenças no ruído, em campo livre, foram obtidos nessas relações sinal/ruído: 0° - 0° = -7,56 dB; -0º - 90º = -11,11 dB; -0º - 180° = -9,75 dB; 0º - 270º = -10,43 dB. Os melhores limiares no ruído foram obtidos com os ângulos de incidência de 0º - 90º e 0º - 270º, seguidos pela condição de 0º - 180º e, por último, 0º - 0º. A condição de escuta no ruído mais desfavorável foi aquela na qual o ruído encontra-se no mesmo ângulo de incidência da fala, na posição frontal do indivíduo avaliado.

Translated abstract

PURPOSE: To determine and compare the sentence recognition thresholds in the noise, in sound field, in the presence of incident noise from different angles, and to verify the most unfavorable hearing condition, in normal-hearing individuals. METHODS: The Portuguese Sentences Lists test was carried out in 38 young adults, evaluated in acoustic booth. The sentences were presented at 0º - 0º azimuth, and the competitive noise at 0º - 0°, 0° - 90°, 0° - 180°, and 0° - 270° azimuth, in a fixed loudness of 65 dB NPS (A). RESULTS: The signal-to-noise ratios in which the sentence recognition thresholds were obtained for these incidence angles were, respectively: -7.56, -11.11, -9.45, and -10.43 dB. Differences were found between the results in the conditions: 0º - 0º and 0º - 90º; 0º - 0º and 0º - 180º; -0º - 0º and 0º - 270º. CONCLUSION: The following sentence recognition thresholds in the noise, in sound field, were obtained for these signal-to-noise ratios: 0° - 0° = -7.56 dB; -0º - 90º = -11.11 dB; -0º - 180° = -9.75 dB; 0º - 270º = -10.43 dB. The better thresholds were obtained with the incidence angles of 0º - 90º and 0º - 270º, followed by the 0º - 180º condition, and, finally, by the 0º - 0º condition. The most unfavorable hearing condition was that in which the noise was in the same incidence angle of the speech, in front of the evaluated subject.

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Development of the Hearing in Noise Test for the measurement of speech reception thresholds in quiet and in noise.

M. Nilsson, S D Soli, J A Sullivan (1994)

A large set of sentence materials, chosen for their uniformity in length and representation of natural speech, has been developed for the measurement of sentence speech reception thresholds (sSRTs). The mean-squared level of each digitally recorded sentence was adjusted to equate intelligibility when presented in spectrally matched noise to normal-hearing listeners. These materials were cast into 25 phonemically balanced lists of ten sentences for adaptive measurement of sentence sSRTs. The 95% confidence interval for these measurements is +/- 2.98 dB for sSRTs in quiet and +/- 2.41 dB for sSRTs in noise, as defined by the variability of repeated measures with different lists. Average sSRTs in quiet were 23.91 dB(A). Average sSRTs in 72 dB(A) noise were 69.08 dB(A), or -2.92 dB signal/noise ratio. Low-pass filtering increased sSRTs slightly in quiet and noise as the 4- and 8-kHz octave bands were eliminated. Much larger increases in SRT occurred when the 2-kHz octave band was eliminated, and bandwidth dropped below 2.5 kHz. Reliability was not degraded substantially until bandwidth dropped below 2.5 kHz. The statistical reliability and efficiency of the test suit it to practical applications in which measures of speech intelligibility are required.

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Effects of fluctuating noise and interfering speech on the speech-reception threshold for impaired and normal hearing.

J Festen, R Plomp (1990)

The speech-reception threshold (SRT) for sentences presented in a fluctuating interfering background sound of 80 dBA SPL is measured for 20 normal-hearing listeners and 20 listeners with sensorineural hearing impairment. The interfering sounds range from steady-state noise, via modulated noise, to a single competing voice. Two voices are used, one male and one female, and the spectrum of the masker is shaped according to these voices. For both voices, the SRT is measured as well in noise spectrally shaped according to the target voice as shaped according to the other voice. The results show that, for normal-hearing listeners, the SRT for sentences in modulated noise is 4-6 dB lower than for steady-state noise; for sentences masked by a competing voice, this difference is 6-8 dB. For listeners with moderate sensorineural hearing loss, elevated thresholds are obtained without an appreciable effect of masker fluctuations. The implications of these results for estimating a hearing handicap in everyday conditions are discussed. By using the articulation index (AI), it is shown that hearing-impaired individuals perform poorer than suggested by the loss of audibility for some parts of the speech signal. Finally, three mechanisms are discussed that contribute to the absence of unmasking by masker fluctuations in hearing-impaired listeners. The low sensation level at which the impaired listeners receive the masker seems a major determinant. The second and third factors are: reduced temporal resolution and a reduction in comodulation masking release, respectively.