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: 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: This study tested the hypothesis that the reduction in spatial release from masking (SRM) resulting from sensorineural hearing loss in competing speech mixtures is influenced by the characteristics of the interfering speech. A frontal speech target was presented simultaneously with two intelligible or two time-reversed (unintelligible) speech maskers that were either colocated with the target or were symmetrically separated from the target in the horizontal plane. The difference in SRM between listeners with hearing impairment and listeners with normal hearing was substantially larger for the forward maskers (deficit of 5.8 dB) than for the reversed maskers (deficit of 1.6 dB). This was driven by the fact that all listeners, regardless of hearing abilities, performed similarly (and poorly) in the colocated condition with intelligible maskers. The same conditions were then tested in listeners with normal hearing using headphone stimuli that were degraded by noise vocoding. Reducing the number of available spectral channels systematically reduced the measured SRM, and again, more so for forward (reduction of 3.8 dB) than for reversed speech maskers (reduction of 1.8 dB). The results suggest that non-spatial factors can strongly influence both the magnitude of SRM and the apparent deficit in SRM for listeners with impaired hearing.The Journal of the Acoustical Society of America 04/2012; 131(4):3103-10. · 1.65 Impact Factor
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ABSTRACT: Speech perception in background noise is a common challenge across individuals and health conditions (e.g., hearing impairment, aging, etc.). Both behavioral and physiological measures have been used to understand the important factors that contribute to perception-in-noise abilities. The addition of a physiological measure provides additional information about signal-in-noise encoding in the auditory system and may be useful in clarifying some of the variability in perception-in-noise abilities across individuals. Fifteen young normal-hearing individuals were tested using both electrophysiology and behavioral methods as a means to determine (1) the effects of signal-to-noise ratio (SNR) and signal level and (2) how well cortical auditory evoked potentials (CAEPs) can predict perception in noise. Three correlation/regression approaches were used to determine how well CAEPs predicted behavior. Main effects of SNR were found for both electrophysiology and speech perception measures, while signal level effects were found generally only for speech testing. These results demonstrate that when signals are presented in noise, sensitivity to SNR cues obscures any encoding of signal level cues. Electrophysiology and behavioral measures were strongly correlated. The best physiological predictors (e.g., latency, amplitude, and area of CAEP waves) of behavior (SNR at which 50 % of the sentence is understood) were N1 latency and N1 amplitude measures. In addition, behavior was best predicted by the 70-dB signal/5-dB SNR CAEP condition. It will be important in future studies to determine the relationship of electrophysiology and behavior in populations who experience difficulty understanding speech in noise such as those with hearing impairment or age-related deficits.Journal of the Association for Research in Otolaryngology 09/2013; · 2.95 Impact Factor