Factors responsible for remote-frequency masking in children and adults

Effect of Masker Head Orientation, Listener Age, and Extended High-Frequency Sensitivity on Speech Recognition in Spatially Separated Speech

OBJECTIVES

Masked speech recognition is typically assessed as though the target and background talkers are all directly facing the listener. However, background speech in natural environments is often produced by talkers facing other directions, and talker head orientation affects the spectral content of speech, particularly at the extended high frequencies (EHFs; >8 kHz). This study investigated the effect of masker head orientation and listeners' EHF sensitivity on speech-in-speech recognition and spatial release from masking in children and adults.

DESIGN

Participants were 5- to 7-year-olds (n = 15) and adults (n = 34), all with normal hearing up to 8 kHz and a range of EHF hearing thresholds. Speech reception thresholds (SRTs) were measured for target sentences recorded from a microphone directly in front of the talker's mouth and presented from a loudspeaker directly in front of the listener, simulating a target directly in front of and facing the listener. The maskers were two streams of concatenated words recorded from a microphone located at either 0° or 60° azimuth, simulating masker talkers facing the listener or facing away from the listener, respectively. Maskers were presented in one of three spatial conditions: co-located with the target, symmetrically separated on either side of the target (+54° and -54° on the horizontal plane), or asymmetrically separated to the right of the target (both +54° on the horizontal plane).

RESULTS

Performance was poorer for the facing than for the nonfacing masker head orientation. This benefit of the nonfacing masker head orientation, or head orientation release from masking (HORM), was largest under the co-located condition, but it was also observed for the symmetric and asymmetric masker spatial separation conditions. SRTs were positively correlated with the mean 16-kHz threshold across ears in adults for the nonfacing conditions but not for the facing masker conditions. In adults with normal EHF thresholds, the HORM was comparable in magnitude to the benefit of a symmetric spatial separation of the target and maskers. Although children benefited from the nonfacing masker head orientation, their HORM was reduced compared to adults with normal EHF thresholds. Spatial release from masking was comparable across age groups for symmetric masker placement, but it was larger in adults than children for the asymmetric masker.

CONCLUSIONS

Masker head orientation affects speech-in-speech recognition in children and adults, particularly those with normal EHF thresholds. This is important because masker talkers do not all face the listener under most natural listening conditions, and assuming a midline orientation would tend to overestimate the effect of spatial separation. The benefits associated with EHF audibility for speech-in-speech recognition may warrant clinical evaluation of thresholds above 8 kHz.

Speech-in-Speech Recognition and Spatially Selective Attention in Children and Adults

Purpose Knowing target location can improve adults' speech-in-speech recognition in complex auditory environments, but it is unknown whether young children listen selectively in space. This study evaluated masked word recognition with and without a pretrial cue to location to characterize the influence of listener age and masker type on the benefit of spatial cues. Method Participants were children (5-13 years of age) and adults with normal hearing. Testing occurred in a 180° arc of 11 loudspeakers. Targets were spondees produced by a female talker and presented from a randomly selected loudspeaker; that location was either known, based on a pretrial cue, or unknown. Maskers were two sequences comprising spondees or speech-shaped noise bursts, each presented from a random loudspeaker. Speech maskers were produced by one male talker or by three talkers, two male and one female. Results Children and adults benefited from the pretrial cue to target location with the three-voice masker, and the magnitude of benefit increased with increasing child age. There was no benefit of location cues in the one-voice or noise-burst maskers. Incorrect responses in the three-voice masker tended to correspond to masker words produced by the female talker, and in the location-known condition, those masker intrusions were more likely near the cued loudspeaker for both age groups. Conclusions Increasing benefit of the location cue with increasing child age in the three-voice masker suggests maturation of spatially selective attention, but error patterns do not support this idea. Differences in performance in the location-unknown condition could play a role in the differential benefit of the location cue.

Development of temporal auditory processing in childhood: Changes in efficiency rather than temporal-modulation selectivity

The ability to detect amplitude modulation (AM) is essential to distinguish the spectro-temporal features of speech from those of a competing masker. Previous work shows that AM sensitivity improves until 10 years of age. This may relate to the development of sensory factors (tuning of AM filters, susceptibility to AM masking) or to changes in processing efficiency (reduction in internal noise, optimization of decision strategies). To disentangle these hypotheses, three groups of children (5-11 years) and one of young adults completed psychophysical tasks measuring thresholds for detecting sinusoidal AM (with a rate of 4, 8, or 32 Hz) applied to carriers whose inherent modulations exerted different amounts of AM masking. Results showed that between 5 and 11 years, AM detection thresholds improved and that susceptibility to AM masking slightly increased. However, the effects of AM rate and carrier were not associated with age, suggesting that sensory factors are mature by 5 years. Subsequent modelling indicated that reducing internal noise by a factor 10 accounted for the observed developmental trends. Finally, children's consonant identification thresholds in noise related to some extent to AM sensitivity. Increased efficiency in AM detection may support better use of temporal information in speech during childhood.

Amplitude modulation detection and modulation masking in school-age children and adults

Two experiments were performed to better understand on- and off-frequency modulation masking in normal-hearing school-age children and adults. Experiment 1 estimated thresholds for detecting 16-, 64- or 256-Hz sinusoidal amplitude modulation (AM) imposed on a 4300-Hz pure tone. Thresholds tended to improve with age, with larger developmental effects for 64- and 256-Hz AM than 16-Hz AM. Detection of 16-Hz AM was also measured with a 1000-Hz off-frequency masker tone carrying 16-Hz AM. Off-frequency modulation masking was larger for younger than older children and adults when the masker was gated with the target, but not when the masker was continuous. Experiment 2 measured detection of 16- or 64-Hz sinusoidal AM carried on a bandpass noise with and without additional on-frequency masker AM. Children and adults demonstrated modulation masking with similar tuning to modulation rate. Rate-dependent age effects for AM detection on a pure-tone carrier are consistent with maturation of temporal resolution, an effect that may be obscured by modulation masking for noise carriers. Children were more susceptible than adults to off-frequency modulation masking for gated stimuli, consistent with maturation in the ability to listen selectively in frequency, but the children were not more susceptible to on-frequency modulation masking than adults.

The Evolution of Statistical Methods in Speech, Language, and Hearing Sciences

Purpose Scientists in the speech, language, and hearing sciences rely on statistical analyses to help reveal complex relationships and patterns in the data collected from their research studies. However, data from studies in the fields of communication sciences and disorders rarely conform to the underlying assumptions of many traditional statistical methods. Fortunately, the field of statistics provides many mature statistical techniques that can be used to meet today's challenges involving complex studies of behavioral data from humans. In this review article, we highlight several techniques and general approaches with promising application to analyses in the speech and hearing sciences. Method The goal of this review article is to provide an overview of potentially underutilized statistical methods with promising application in the speech, language, and hearing sciences. Results We offer suggestions to identify when alternative statistical approaches might be advantageous when analyzing proportion data and repeated measures data. We also introduce the Bayesian paradigm and statistical learning and offer suggestions for when a scientist might consider those methods. Conclusion Modern statistical techniques provide more flexibility and enable scientists to ask more direct and informative research questions.

Speech recognition for school-age children and adults tested in multi-tone vs multi-noise-band maskers

The present study set out to test whether greater susceptibility to modulation masking could be responsible for immature recognition of speech in noise for school-age children. Listeners were normal-hearing four- to ten-year-olds and adults. Target sentences were filtered into 28 adjacent narrow bands (100-7800 Hz), and the masker was either spectrally matched noise bands or tones centered on each of the speech bands. In experiment 1, odd- and even-numbered bands of target-plus-masker were presented to opposite ears. Performance improved with child age in all conditions, but this improvement was larger for the multi-tone than the multi-noise-band masker. This outcome is contrary to the expectation that children are more susceptible than adults to masking produced by inherent modulation of the noise masker. In experiment 2, odd-numbered bands were presented to both ears, with the masker diotic and the target either diotic or binaurally out of phase. The binaural difference cue was particularly beneficial for young children tested in the multi-tone masker, suggesting that development of auditory stream segregation may play a role in the child-adult difference for this condition. Overall, results provide no evidence of greater susceptibility to modulation masking in children than adults.

The Effect of Remote Masking on the Reception of Speech by Young School-Age Children

PURPOSE

Psychoacoustic data indicate that infants and children are less likely than adults to focus on a spectral region containing an anticipated signal and are more susceptible to remote masking of a signal. These detection tasks suggest that infants and children, unlike adults, do not listen selectively. However, less is known about children's ability to listen selectively during speech recognition. Accordingly, the current study examines remote masking during speech recognition in children and adults.

METHOD

Adults and 7- and 5-year-old children performed sentence recognition in the presence of various spectrally remote maskers. Intelligibility was determined for each remote-masker condition, and performance was compared across age groups.

RESULTS

It was found that speech recognition for 5-year-olds was reduced in the presence of spectrally remote noise, whereas the maskers had no effect on the 7-year-olds or adults. Maskers of different bandwidth and remoteness had similar effects.

CONCLUSIONS

In accord with psychoacoustic data, young children do not appear to focus on a spectral region of interest and ignore other regions during speech recognition. This tendency may help account for their typically poorer speech perception in noise. This study also appears to capture an important developmental stage, during which a substantial refinement in spectral listening occurs.