Speech recognition in fluctuating and continuous maskers: effects of hearing loss and presentation level.
ABSTRACT Listeners with normal-hearing sensitivity recognize speech more accurately in the presence of fluctuating background sounds, such as a single competing voice, than in unmodulated noise at the same overall level. These performance differences are greatly reduced in listeners with hearing impairment, who generally receive little benefit from fluctuations in masker envelopes. If this lack of benefit is entirely due to elevated quiet thresholds and the resulting inaudibility of low-amplitude portions of signal + masker, then listeners with hearing impairment should derive increasing benefit from masker fluctuations as presentation levels increase. Listeners with normal-hearing (NH) sensitivity and listeners with hearing impairment (HI) were tested for sentence recognition at moderate and high presentation levels in competing speech-shaped noise, in competing speech by a single talker, and in competing time-reversed speech by the same talker. NH listeners showed more accurate recognition at moderate than at high presentation levels and better performance in fluctuating maskers than in unmodulated noise. For these listeners, modulated versus unmodulated performance differences tended to decrease at high presentation levels. Listeners with HI, as a group, showed performance that was more similar across maskers and presentation levels. Considered individually, only 2 out of 6 listeners with HI showed better overall performance and increasing benefit from masker fluctuations as presentation level increased. These results suggest that audibility alone does not completely account for the group differences in performance with fluctuating maskers; suprathreshold processing differences between groups also appear to play an important role. Competing speech frequently provided more effective masking than time-reversed speech containing temporal fluctuations of equal magnitude. This finding is consistent with "informational" masking resulting from competitive processing of words and phrases within the speech masker that would notoccur for time-reversed sentences.
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ABSTRACT: OBJETIVO: Este estudo investigou o efeito das diferentes taxas de modulações do mascaramento na magnitude do masking release. MÉTODOS: Quinze indivíduos jovens, com audição normal, foram submetidos ao teste de reconhecimento de sentença na presença de ruído, utilizando as listas de sentenças do HINT-Brasil. Foram obtidos limiares de reconhecimento de fala em presença de ruído estável e ruído modulado, em diferentes taxas de modulação (4, 8, 16, 32 e 64 Hz). A magnitude do masking release foi obtida para cada modulação e foi realizada a análise comparativa dos resultados. RESULTADOS: Os achados demonstraram melhores limiares de reconhecimento de sentenças quando o ruído mascarante foi modulado em 4, 8, 16 e 32 Hz e piores limiares quando o ruído mascarante estava estável e em 64 Hz. No que diz respeito à análise da relação sinal/ruído, foram observados, no presente estudo, maiores valores para as tarefas que envolvem reconhecimento de sentenças com ruído estável, seguidos das tarefas que envolvem reconhecimento de sentenças com ruído modulado em 64 Hz, e menores valores para as tarefas que envolvem reconhecimento de sentenças com ruído modulado em 32, 16, 8 e 4 Hz, respectivamente. CONCLUSÃO: A magnitude do masking release para sentenças não se diferencia com taxas de modulação em amplitude entre 4 e 32 Hz. No entanto, quando a taxa de modulação é elevada a 64 Hz, a magnitude do masking release diminui.Audiology - Communication Research. 12/2013; 18(4):238-244.
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ABSTRACT: Howard-Jones and Rosen [(1993). J. Acoust. Soc. Am. 93, 2915-2922] investigated the ability to integrate glimpses of speech that are separated in time and frequency using a "checkerboard" masker, with asynchronous amplitude modulation (AM) across frequency. Asynchronous glimpsing was demonstrated only for spectrally wide frequency bands. It is possible that the reduced evidence of spectro-temporal integration with narrower bands was due to spread of masking at the periphery. The present study tested this hypothesis with a dichotic condition, in which the even- and odd-numbered bands of the target speech and asynchronous AM masker were presented to opposite ears, minimizing the deleterious effects of masking spread. For closed-set consonant recognition, thresholds were 5.1-8.5 dB better for dichotic than for monotic asynchronous AM conditions. Results were similar for closed-set word recognition, but for open-set word recognition the benefit of dichotic presentation was more modest and level dependent, consistent with the effects of spread of masking being level dependent. There was greater evidence of asynchronous glimpsing in the open-set than closed-set tasks. Presenting stimuli dichotically supported asynchronous glimpsing with narrower frequency bands than previously shown, though the magnitude of glimpsing was reduced for narrower bandwidths even in some dichotic conditions.The Journal of the Acoustical Society of America 08/2012; 132(2):1152-64. · 1.65 Impact Factor
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ABSTRACT: Infants are often spoken to in the presence of background sounds, including speech from other talkers. In the present study, we compared 5- and 8.5-month-olds' abilities to recognize their own names in the context of three different types of background speech: that of a single talker, multitalker babble, and that of a single talker played backward. Infants recognized their names at a 10-dB signal-to-noise ratio in the multiple-voice condition but not in the single-voice (nonreversed) condition, a pattern opposite to that of typical adult performance. Infants similarly failed to recognize their names when the background talker's voice was reversed--that is, unintelligible, but with speech-like acoustic properties. These data suggest that infants may have difficulty segregating the components of different speech streams when those streams are acoustically too similar. Alternatively, infants' attention may be drawn to the time-varying acoustic properties associated with a single talker's speech, causing difficulties when a single talker is the competing sound.Attention Perception & Psychophysics 06/2009; 71(4):822-36. · 1.97 Impact Factor