Speech Recognition in Fluctuating and Continuous Maskers: Effects of Hearing Loss and Presentation Level
Walter Reed National Military Medical Center, Washington, Washington, D.C., United StatesJournal of Speech Language and Hearing Research (Impact Factor: 2.07). 05/2004; 47(2):245-56. DOI: 10.1044/1092-4388(2004/020)
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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- "), this does not indicate the extent to which amplification restores masking release for participants with hearing loss. Many studies that compared participants with hearing loss to participants with normal hearing (Bernstein & Grant, 2009; Hall et al 2012; Lorenzi, et al 2006; Summers & Molis, 2004) did not apply frequency-shaped amplification. Therefore, parts of the signal may not have been audible for some frequencies during the dips in the masker level. "
ABSTRACT: Purpose: This study compared masking release for adults and children with normal hearing and hearing loss. For the participants with hearing loss, masking release using simulated hearing aids with two different compression speeds (slow, fast) was compared. Methods: Sentence recognition in unmodulated noise was compared to recognition in modulated noise (masking release). Recognition was measured for participants with hearing loss using individualized amplification via a hearing-aid simulator. Results: Adults with hearing loss showed greater masking release than the children with hearing loss. Average masking release was small (1 dB) and did not depend on hearing status. Masking release was comparable for slow and fast compression. Conclusion: The use of amplification in this study contrasts with previous studies that did not apply amplification and suggests that when differences in audibility are reduced, participants with hearing loss may be able to take similar advantage of dips in the noise levels as participants with normal hearing. While children required a more favorable signal-to-noise ratio than adults for both unmodulated and modulated noise, masking release was not statistically different. However, the ability to detect a difference may have been limited by the small amount of masking release observed.
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- "The current findings with young children, similar to that with adults (e.g., Summers and Molis, 2004; Brouwer et al., 2012), suggest that at least some of this IM may be the result of lexical competition between target and masker speech. Furthermore, the language development that presumably underlies this effect appears to be intact by 4 yrs of age (the mean age of our preschool group). "
ABSTRACT: Previous work has shown that young children exhibit more difficulty understanding speech in the presence of speech-like distractors than do adults, and are more susceptible to at least some form of informational masking (IM). Yet little is known about how/when the "susceptibility" to linguistically-based IM develops. The authors tested adults, school-age children (aged 8 yrs), and preschool-age children (aged 4 yrs) on sentence recognition in the presence of normal speech, "jumbled" speech, and reversed speech distractors. As has been found previously with adults [e.g., Summers and Molis (2004). J. Speech, Lang. Hear. Res. 47, 245-256], children in both age groups showed a release of masking when the distractor was uninterpretable (reversed speech). This suggests that children already demonstrate linguistically-based IM by the age of 4 yrs.
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- "The optimal rate of modulation has been shown to depend on the type of speech material and the number of possible response alternatives (Buss et al., 2009). In addition to studies that have found modulation rate to be an important parameter (Miller and Licklider, 1950; Buss et al., 2009), the amount of masking release incurred by introducing masker amplitude modulation (AM) is larger for deeper masker modulation depth (Gnansia et al., 2008), and for more intense maskers (Summers and Molis, 2004; George et al., 2006). Whereas most studies of masker fluctuation have evaluated envelope fluctuations that are coherent across frequency , naturally occurring maskers often contain spectrotemporally complex fluctuations. "
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.
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