Jean Sullivan

Development of the Hearing In Noise Test for the measurement of speech reception thresholds in quiet and in noise

A large set of sentence materials, chosen for their uniformity in length and representation of natural speech, has been developed for the measurement of sentence speech reception thresholds (sSRTs). The mean-squared level of each digitally recorded sentence was adjusted to equate intelligibility when presented in spectrally matched noise to normal-hearing listeners. These materials were cast into 25 phonemically balanced lists of ten sentences for adaptive measurement of sentence sSRTs. The 95% confidence interval for these measurements is +/- 2.98 dB for sSRTs in quiet and +/- 2.41 dB for sSRTs in noise, as defined by the variability of repeated measures with different lists. Average sSRTs in quiet were 23.91 dB(A). Average sSRTs in 72 dB(A) noise were 69.08 dB(A), or -2.92 dB signal/noise ratio. Low-pass filtering increased sSRTs slightly in quiet and noise as the 4- and 8-kHz octave bands were eliminated. Much larger increases in SRT occurred when the 2-kHz octave band was eliminated, and bandwidth dropped below 2.5 kHz. Reliability was not degraded substantially until bandwidth dropped below 2.5 kHz. The statistical reliability and efficiency of the test suit it to practical applications in which measures of speech intelligibility are required.

Method of signal processing for maintaining directional hearing with hearing aids

The insertion effects of hearing aids are determined and compensated to restore the ability to have directional hearing in individuals wearing hearing aids. In one aspect a method involves finding the ratio of the unaided head related transfer function to the aided head related transfer function and then designing a hearing aid filter that is the inverse of that derived insertion effect, thereby restoring the ability to hear interaural differences in aided systems both in level and in time of arrival to improve hearing in the presence of noise. The insertion effects can be derived either through frequency domain analyses, using the above-mentioned transfer function calculations and measurements, or in another aspect through time domain analyses, using optimal filter calculations and measurement obtained using a successive data acquisition system that is subsequently time aligned by recording trigger pulses with the data.

An experimental comparison of four hearing aid prescription methods.

Four hearing aid prescription methods were compared. A digital master hearing aid was used to produce the prescribed frequency gain characteristics. Measures of speech recognition and paired comparison judgments of relative speech intelligibility and speech quality were obtained at three output levels for each of the experimental frequency gain characteristics. No single prescriptive method emerged as being clearly superior. Relative performance of the four prescriptive methods varied as a function of output level. Similar results were observed for both speech recognition testing and paired comparison testing.

Factors affecting children’s speech communication in classrooms

A child’s ability to hear and communicate with speech in the classroom is influenced by several factors, including talker characteristics (level, clarity, dialect), the acoustical environment (noise level, reverberance), and listener characteristics (hearing status, cognitive development, language level, exposure to English). This presentation will review and assess the relative contribution of each factor to the communication requirements of the classroom. An emphasis will be placed on the large individual differences in listener characteristics that are likely to exist in contemporary classrooms, and their impact on the requirements of the acoustic environment for effective speech communication. Recent findings from this laboratory and from other researchers that document the range of speech communication abilities in both difficult and easy listening conditions among school‐age children will be reviewed. Finally, an initial proposal for acceptable levels of background noise and reverberance in classroo...

Norms for the hearing in noise test: The influence of spatial separation, hearing loss, and English language experience on speech reception thresholds

Norms have been developed for the hearing in noise test [Nilsson et al., J. Acoust. Soc. Am. Suppl. 1 88, S175 (1990)]. Speech reception thresholds (SRTs) were measured adaptively in the presence of spectrally matched noise for 150 young male and female adults. Speech was presented at 0‐deg azimuth in all conditions, and noise was presented at either 0‐, 90‐, or 270‐deg azimuth at 65 dB(A). Pure‐tone thresholds were measured at 0.5, 1, 2, 3, 4, 6, and 8 kHz. Subjects were also characterized according to their early language acquisition experience with English in one of five categories ranging from ‘‘English only’’ to ‘‘no English in the home.’’ Average SRTs for normal‐hearing, ‘‘English only’’ subjects (pure‐tone thresholds at all frequencies tested of 15 dB HL or better) noise equaled 62.26 dB(A) (−2.74 dB S/N). Several factors significantly influence thresholds: (1) spatial separation between the speech and noise lowered thresholds an average of 7.42 dB; (2) unilateral, high‐frequency hearing loss eleva...

Measurement and predictions of hearing handicap using an additive noise model.

The ability to accurately, quickly, and reliably measure speech intelligibility in noise is an essential requirement for assessing the benefit of hearing aids to speech communication in noisy environments. Measurement error caused by variability of speech materials, content, speaking styles, talkers, and spectral characteristics of noise maskers often make accurate intelligibility measurements impractical. This paper will review measurements of speech intelligibility as applied to the hearing impaired. Emphasis will be placed on Dutch sentence tests developed by Plomp [e.g., R. Plomp, J. Acoust. Soc. Am. 63, 533–549 (1978)] and on recent English sentence tests we have developed, which control many of the sources of measurement error. Test development procedures will be described, and a summary of initial results will be used to demonstrate the reliability of the tests for both group and individual assessment of intelligibility in noise.

Validation of a speech intelligibility test using SRT for hearing aid research

Speech reception thresholds (SRT) were measured in the presence of spectrally matched masking noise using an English language speech comprehension test that has been developed to address some shortcomings of current speech tests as measures of hearing handicap [M. J. Nilsson et al., J. Acoust. Soc. Am. Suppl. 1 88, S175 (1990)]. Following procedures used with Dutch materials [R. Plomp and A. M. Mimpen, Audiology 18, 43–52 (1979)], Leq of the sentence materials was matched and then adjusted to compensate for relative differences in difficulty between sentences. Lists of 12 sentences were created with nearly equal distribution of phonemes. SRTs were measured using normal‐hearing subjects with unmodified as well as high‐ and low‐pass filtered conditions in an effort to measure the repeatability of the lists for different signal bandwidths. Results of these tests will be presented and the use of these materials in hearing aid research will be discussed.

Development of a speech intelligibility test for hearing aid research

An English language speech comprehension test has been developed to address shortcomings of current speech tests as measures of hearing handicap [R. Plomp, J. Acoust. Soc. Am. 63, 533–549 (1979)]. The Bamford‐Kowal‐Bench sentences, as revised to conform to American English usage, were modified to create 28 lists of 12 sentences of approximately equivalent length, difficulty, and phonetic content. These materials were then sampled at 20 kHz with 8‐kHz bandwidth for measurement, editing, and analysis. Following procedures used with Dutch materials [R. Plomp and A. M. Mimpen, Audiology 18, 43–52 (1979)], L eq for each sentence was matched as closely as possible. Speech reception thresholds were measured in the presence of masking noise that matched the average long‐term spectrum of all sentences as a means of norming the difficulty of each sentence list. Results of the norming tests will be presented and the use of these materials in hearing aid research will be discussed.

Discriminability of frequency‐response irregularities in hearing aids

Frequency‐gain characteristics of a large number of hearing aids were measured using a computer‐based system for the automated measurement of hearing aids [Levitt and Sullivan, Hear. Instrum. 37, 16–18 (1986)]. Irregularities in the frequency‐gain characteristic were specified in terms of the peak‐valley ratio and bandwidth of each spectral peak. Typical frequency‐response irregularities were then simulated on a digital master hearing aid and the detectability of both single and multiple peaks was measured using an adaptive paired‐comparison technique. The average peak‐valley detection threshold for single peaks was approximately 6 dB for normal‐hearing subjects and 11 dB for hearing‐impaired subjects. The average detection threshold for a typical set of four multiple peaks was approximately 6 dB for hearing‐impaired subjects. [Research supported by NIHR.]

Assessment of the classroom as a communication channel

The classroom is an environment in which spoken language communication facilitates and enables students in the learning of essential academic, social, and cultural skills. As such, the classroom defines a communication channel for learning. Our research has focused on the special requirements placed on this communication channel by the student listener. Our strategy is to quantify the effects of age, developmental status, hearing status, and English proficiency on speech intelligibility in noise and to find the signal/noise ratios that enable all students to obtain high intelligibility. Using these signal/noise ratios, acceptable noise levels and reverberation times for the classroom communication channel are estimated. Our studies of young children for whom English is either the primary language (EPL) or the secondary language (ESL) will be reported. The method of estimating the special requirements these children place on the classroom communication channel will also be described. Acoustic measurements ...