Peggy B. Nelson

Background Noise Levels and Reverberation Times in Unoccupied Classrooms: Predictions and Measurements

Classrooms are often filled with deterrents that hamper a childs ability to listen and learn. It is evident that the acoustical environment in classrooms can be one such deterrent. Excessive background noise and reverberation can affect the achievement and educational performance of children with sensorineural hearing loss (SNHL) and children with normal hearing sensitivity who have other auditory learning difficulties, as well as elementary school children with no verbal or hearing disabilities. The purpose of this study was to evaluate the extent of the problem of noise and reverberation in schools. To that end, we measured reverberation times and background noise levels in 32 different unoccupied elementary classrooms in eight public school buildings in central Ohio. The results were compared with the limits recommended in the American National Standards Institute standard for acoustical characteristics of classrooms in the United States (ANSI S12.60-2002). These measurements were also compared to the external and internal criteria variables developed by Crandell, Smaldino, & Flexer (1995) to determine if a simple checklist can accurately predict unwanted classroom background noise levels and reverberation. Results indicated that most classrooms were not in compliance with ANSI noise and reverberation standards. Further, our results suggested that a checklist was not a good predictor of the noisier and more reverberant rooms.

Acoustical Barriers To Learning: Children at Risk in Every Classroom.

There are surprisingly large numbers of children with various auditory disorders in the schools. Their classrooms are often noisy, reverberant, and active places of learning. For these children, their auditory problems plus the poor classroom acoustics cause significant learning problems. Poor listening conditions can affect all children, but they affect those with auditory disorders more. Improving classroom acoustics can significantly reduce the negative educational impact of auditory disorders. This article reviews relevant literature on acoustical barriers to successful learning and provides guidance for school personnel making decisions regarding classroom facilities.

Speech perception in gated noise: The effects of temporal resolution

Previous investigations have suggested that hearing-impaired (HI) listeners have reduced masking release (MR) compared to normal hearing listeners (NH) when they listen in modulated noise. The current study examined the following questions that have not been clearly answered: First, when HI listeners are amplified so that their performance is equal to that of NH listeners in quiet and in steady noise, do HI listeners still show reduced MR with modulated noise when compared to NH listeners? Second, is the masking release the same for sentences and CV syllables? Third, does forward masking significantly contribute to the variability in performance among HI listeners? To compensate for reduced hearing sensitivity for HI listeners, the spectrum levels of both speech and noise were adjusted based on the individual hearing loss. There was no significant difference between the performance of NH listeners and that of HI listeners in steady noise and in quiet. However, the amount of MR for sentences and for CV syllables was significantly reduced for HI listeners. For sentence recognition, the amount of MR seemed to be more related to hearing sensitivity for low-to-mid frequencies than to forward masking. In contrast, forward masking thresholds appear to be a major contributor to the amount of MR for syllable recognition.

Comparing spatial tuning curves, spectral ripple resolution, and speech perception in cochlear implant users.

Spectral ripple discrimination thresholds were measured in 15 cochlear-implant users with broadband (350-5600 Hz) and octave-band noise stimuli. The results were compared with spatial tuning curve (STC) bandwidths previously obtained from the same subjects. Spatial tuning curve bandwidths did not correlate significantly with broadband spectral ripple discrimination thresholds but did correlate significantly with ripple discrimination thresholds when the rippled noise was confined to an octave-wide passband, centered on the STCs probe electrode frequency allocation. Ripple discrimination thresholds were also measured for octave-band stimuli in four contiguous octaves, with center frequencies from 500 Hz to 4000 Hz. Substantial variations in thresholds with center frequency were found in individuals, but no general trends of increasing or decreasing resolution from apex to base were observed in the pooled data. Neither ripple nor STC measures correlated consistently with speech measures in noise and quiet in the sample of subjects in this study. Overall, the results suggest that spectral ripple discrimination measures provide a reasonable measure of spectral resolution that correlates well with more direct, but more time-consuming, measures of spectral resolution, but that such measures do not always provide a clear and robust predictor of performance in speech perception tasks.

Phonetic identification in quiet and in noise by listeners with cochlear implants

This study examined the effect of noise on the identification of four synthetic speech continua (/ra/-/la/, /wa/-/ja/, /i/-/u/, and say-stay) by adults with cochlea implants (CIs) and adults with normal-hearing (NH) sensitivity in quiet and noise. Significant group-by-SNR interactions were found for endpoint identification accuracy for all continua except /i/-/u/. The CI listeners showed the least NH-like identification functions for the /ra/-/la/ and /wa/-/ja/ continua. In a second experiment, NH adults identified four- and eight-band cochlear implant stimulations of the four continua, to examine whether group differences in frequency selectivity could account for the group differences in the first experiment. Number of bands and SNR interacted significantly for /ra/-/la/, /wa/-/ja/, and say-stay endpoint identification; strongest effects were found for the /ra/-/la/ and say-stay continua. Results suggest that the speech features that are most vulnerable to misperception in noise by listeners with CIs are those whose acoustic cues are rapidly changing spectral patterns, like the formant transitions in the /wa/-/ja/ and /ra/-/la/ continua. However, the group differences in the first experiment cannot be wholly attributable to frequency selectivity differences, as the number of bands in the second experiment affected performance differently than suggested by group differences in the first experiment.

Behavioral measures of cochlear compression and temporal resolution as predictors of speech masking release in hearing-impaired listeners

Hearing-impaired (HI) listeners often show less masking release (MR) than normal-hearing listeners when temporal fluctuations are imposed on a steady-state masker, even when accounting for overall audibility differences. This difference may be related to a loss of cochlear compression in HI listeners. Behavioral estimates of compression, using temporal masking curves (TMCs), were compared with MR for band-limited (500-4000 Hz) speech and pure tones in HI listeners and age-matched, noise-masked normal-hearing (NMNH) listeners. Compression and pure-tone MR estimates were made at 500, 1500, and 4000 Hz. The amount of MR was defined as the difference in performance between steady-state and 10-Hz square-wave-gated speech-shaped noise. In addition, temporal resolution was estimated from the slope of the off-frequency TMC. No significant relationship was found between estimated cochlear compression and MR for either speech or pure tones. NMNH listeners had significantly steeper off-frequency temporal masking recovery slopes than did HI listeners, and a small but significant correlation was observed between poorer temporal resolution and reduced MR for speech. The results suggest either that the effects of hearing impairment on MR are not determined primarily by changes in peripheral compression, or that the TMC does not provide a sufficiently reliable measure of cochlear compression.

Frequency lowering processing for listeners with significant hearing loss

Many listeners with medium-severe hearing loss present audiograms with high frequency loss descending profiles. These patients can resolve spectral cues normally for lower frequency signals but they often show less ability to use high frequency information. We have presented in this paper a new processing algorithm based on a sinusoidal speech model which results is lowered and sharpened speech. Preliminary results of the processed speech material in two impaired listeners suggests that this algorithm could be implemented in digital hearing aids to be used in patients with severe and moderate-severe hearing loss.

Analysis of Successful Initiations of Three Children With Hearing Loss Mainstreamed in Kindergarten Classrooms

The communicative interactions of three mainstreamed children who are deaf or hard of hearing (deaf/HOH) were investigated. These children were matched with a classmate who had normal hearing (NH) according to chronological age, sex, race, and socioeconomic status (SES). All subjects were white females approximately 5 years of age. The subjects were videotaped while involved in normal classroom activities. The videotaped interactions were coded for: (a) activity, (b) play level, (c) partner, (d) interactive status, and (e) mode of communication. Dyad interactions were analyzed for average length, frequency, and total number of interactions. The children’s interactions varied by child and classroom setting. Results regarding the success of initiations were that one subject who is deaf initiated less often and was more successful than her peer with NH; the other subject who is deaf initiated less often and was less successful than her peer with NH; and the subject who is HOH initiated more often and was les...

Auditory stream segregation using bandpass noises: evidence from event-related potentials

The current study measured neural responses to investigate auditory stream segregation of noise stimuli with or without clear spectral contrast. Sequences of alternating A and B noise bursts were presented to elicit stream segregation in normal-hearing listeners. The successive B bursts in each sequence maintained an equal amount of temporal separation with manipulations introduced on the last stimulus. The last B burst was either delayed for 50% of the sequences or not delayed for the other 50%. The A bursts were jittered in between every two adjacent B bursts. To study the effects of spectral separation on streaming, the A and B bursts were further manipulated by using either bandpass-filtered noises widely spaced in center frequency or broadband noises. Event-related potentials (ERPs) to the last B bursts were analyzed to compare the neural responses to the delay vs. no-delay trials in both passive and attentive listening conditions. In the passive listening condition, a trend for a possible late mismatch negativity (MMN) or late discriminative negativity (LDN) response was observed only when the A and B bursts were spectrally separate, suggesting that spectral separation in the A and B burst sequences could be conducive to stream segregation at the pre-attentive level. In the attentive condition, a P300 response was consistently elicited regardless of whether there was spectral separation between the A and B bursts, indicating the facilitative role of voluntary attention in stream segregation. The results suggest that reliable ERP measures can be used as indirect indicators for auditory stream segregation in conditions of weak spectral contrast. These findings have important implications for cochlear implant (CI) studies—as spectral information available through a CI device or simulation is substantially degraded, it may require more attention to achieve stream segregation.

Neural indices of phonemic discrimination and sentence-level speech intelligibility in quiet and noise: A mismatch negativity study.

Successful speech communication requires the extraction of important acoustic cues from irrelevant background noise. In order to better understand this process, this study examined the effects of background noise on mismatch negativity (MMN) latency, amplitude, and spectral power measures as well as behavioral speech intelligibility tasks. Auditory event-related potentials (AERPs) were obtained from 15 normal-hearing participants to determine whether pre-attentive MMN measures recorded in response to a consonant (from /ba/ to /bu/) and vowel change (from /ba/ to /da/) in a double-oddball paradigm can predict sentence-level speech perception. The results showed that background noise increased MMN latencies and decreased MMN amplitudes with a reduction in the theta frequency band power. Differential noise-induced effects were observed for the pre-attentive processing of consonant and vowel changes due to different degrees of signal degradation by noise. Linear mixed-effects models further revealed significant correlations between the MMN measures and speech intelligibility scores across conditions and stimuli. These results confirm the utility of MMN as an objective neural marker for understanding noise-induced variations as well as individual differences in speech perception, which has important implications for potential clinical applications.