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Thresholds and psychometric functions of the individual spondaic words.

Two experiments were conducted concerning the relative intelligibility of spondaic words. In the first experiment, the 36 spondaic words typically used in clinical settings to determine the Speech-Recognition-Threshold (SRT) were presented to 20 subjects at levels ranging from 10 to 28 dB SPL. The percentage of persons able to repeat each word was plotted as a function of decibel sound-pressure level to determine (a) the sound-pressure level necessary to yield a 50% response point for each word, and (b) the rate at which each word became intelligible, for example, the slope of the psychometric function. By these two criteria 15 words were found to be homogeneous. In the second experiment, SRTs were obtained on 24 subjects with the full list of 36 words and with the 15 spondaic words that were homogeneous with respect to the sound-pressure level necessary for a 50% correct response level and the rate of intelligibility growth. The results demonstrate that the two groups of spondaic words yield equivalent SRTs. The data suggest that an SRT may be determined with 15 spondaic words, which is as valid and accurate as the SRT determined with the entire list of 36 words.

Humans↗

Notched-noise measures of frequency selectivity in adults and children using fixed-masker-level and fixed-signal-level presentation.

Three experiments were performed to examine the development of frequency selectivity and to attempt to separate peripheral versus central contributions to frequency selectivity. In Experiment 1, frequency selectivity was examined in 4-year-old children, 6-year-old children, and adults, using a fixed-masker-level, notched-noise masking method. Thresholds were determined in a no-notch condition and in conditions in which the notchwidth was 0.3 times the center frequency (0.3 x fc) or 0.6 x fc. The results for the adults and 6-year-olds were similar, but the notched-noise functions of the 4-year-old listeners were relatively shallow. These results were consistent with an interpretation that frequency selectivity is relatively poor in 4-year-old listeners; however, the results of the 4-year-old listeners might also be accounted for in terms of poor processing efficiency. For example, the children may require a relatively high level of signal-related excitation in order for detection to occur. If the growth of excitation is steeper in the no-notch condition than in notched-noise conditions, then thresholds in the notched-noise conditions might be elevated because of poor processing efficiency rather than poor frequency selectivity. This interpretation is consonant with past data showing that the growth of loudness of partially masked signals steepens as a function of increasing masker level: The masker level at the output of the auditory filter centered on the signal frequency would be less for the notched-noise masker than for the masker having no notch. In Experiment 2 the growth of loudness was examined for three adult listeners in the no-notch condition and the 0.6 x fc notched noise. Results showed a steeper growth of loudness in the no-notch case. In Experiment 3, a notched-noise measure of frequency selectivity was used in which the signal level was fixed at 15 dB SL and the masker level was varied adaptively. In this method the noise level at the output of the auditory filter centered on the signal should theoretically be constant over the different notch conditions. Adult and 4-year-old listeners were tested. The notched-noise functions were similar between the adult and 4-year-old listeners. This result supports an interpretation that the shallow notched-noise, fixed-masker-level functions of 4-year-old children may be due to poor processing efficiency rather than to poor peripheral frequency selectivity.

Adult↗

Modulation detection in subjects with relatively flat hearing losses.

Modulation detection thresholds were measured as a function of modulation frequency in 5 normal-hearing subjects and in 8 subjects with relatively flat, slight-to-moderate hearing losses. The carrier was a broadband noise that was sinusoidally amplitude modulated (SAM) in one of two observation intervals. The spectrum level of the carrier ranged from -10 to 50 dB SPL, and, for a given carrier level, modulation frequency varied from 2 to 1024 Hz. The temporal modulation transfer functions (TMTFs) were fitted very well with a simple equation describing a low-pass filter function. The TMTFs from the normal-hearing subjects were relatively independent of carrier level, although the derived time constant tended to increase slightly with decreases in carrier level, from an average value of 2.5 msec at 30 dB SPL to 6.0 msec at -10 dB SPL. In addition, sensitivity to amplitude modulation (AM) decreased by about 4 dB as the pressure spectrum level of the carrier was decreased from 0 to -10 dB SPL. The TMTFs from 7 of the 8 hearing-impaired subjects were similar to those from the normal-hearing subjects when the carriers were presented at equal SPLs, except that the derived time constants were slightly larger in the subjects with hearing impairment. When comparisons were made at comparable sensation levels (SLs), however, the TMTFs from the two groups of subjects were quantitatively similar, with the exception that at the lowest SL (20 dB), hearing-impaired subjects typically were more sensitive to AM than normal-hearing subjects, and the derived time constants from their TMTFs were somewhat smaller. These results, taken together with previously published results, suggest that a broad listening bandwidth is important for normal performance on a temporal resolution task. That the time constant from one of the hearing-impaired subjects was significantly longer than normal, regardless of whether the comparisons were made at equal SPL or equal SL, indicates that other factors can also be important.

Adult↗

Auditory dysfunction with facial paralysis.

A series of 58 patients with idiopathic facial paralysis were studied to determine if a concomitant cochlear or eight nerve auditory dysfunction could be identified with traditional audiologic tests. Results indicated that only those patients with a facial nerve lesion, proximal to the stapedius branch, experienced reduced tolerance for loud sounds, reduction of speech discrimination at high-intensity levels, and abnormal loudness growth. Such findings suggest that changes in auditory function, accompanying facial nerve paralysis, are a mechanical effect due to absence of stapedial action. Site of lesion tests in this sample failed to demonstrate eighth nerve dysfunction and, thus, does not support a theory of polyneuropathy that involves the auditory nerve.

Adolescent↗

Design for an inexpensive but effective cochlear implant.

Widespread application of cochlear implants is limited by cost, especially in developing countries. In this article we present a design for a low-cost but effective cochlear implant system. The system includes a speech processor, four pairs of transmitting and receiving coils, and an electrode array with four monopolar electrodes. All implanted components are passive, reducing to a minimum the complexity of manufacture and allowing high reliability. A four-channel continuous interleaved sampling strategy is used for the speech processor. The processor and transmission link have been evaluated in tests with a subject previously implanted with the Ineraid electrode array and percutaneous connector. A prototype of the link, consisting of four pairs of transmitting and external receiving coils, was used, with the outputs of the receiving coils directed to four intracochlear electrodes through the percutaneous connector. The subject achieved speech reception scores with the prototype system that were equivalent to those achieved with a standard laboratory implementation of a continuous interleaved sampling processor with current-controlled stimuli.

Cochlear Implantation↗

A picture identification task as an estimate of the word-recognition performance of nonverbal adults.

The Picture Identification Task was developed to estimate the word-recognition performance of nonverbal adults. Four lists of 50 monosyllabic words each were assembled and recorded. Each test word and three rhyming alternatives were illustrated and photographed in a quadrant arrangement. The task of the patient was to point to the picture representing the recorded word that was presented through the earphone. In the first experiment with young adults, no significant differences were found between the Picture Identification Task and the Northwestern University Auditory Test No. 6 materials in an open-set response paradigm. In the second experiment, the Picture Identification Task with the picture-pointing response was compared with the Northwestern University Auditory Test No. 6 in both an open-set and a closed-set response paradigm. The results from this experiment demonstrated significant differences among the three response tasks. The easiest task was a closed-set response to words, the next was a closed-set response to pictures, and the most difficult task was an open-set response. At high stimulus-presentation levels, however, the three tasks produced similar results. Finally, the clinical use of the Picture Identification Task is described along with preliminary results obtained from 30 patients with various communicative impairments.

Adult↗

Speech audiometry in the young child.

Normal children between 3 and 6 yrs old generated word and sentence messages for use in a pediatric speech intelligibility (PSI) test. Word materials did not differ as a function of chronological age (CA), vocabulary skills, or receptive language (RL) ability. Elicited sentence materials, however, did reflect differences in CA, vocabulary skills, and RL ability. To represent differences in the children's responses, two different types of test sentences, subsequently referred to as format I and format II sentences, were formed. Performance for format I and format II sentences was significantly different in normal children between 3 and 6 yrs old. Performance differences were related to CA and RL ability. However, performance for format I sentences in children with relatively low RL age and performance for format II sentences in children with relatively high RL age was equivalent. This observation yielded an algorithm that determines the sentence format as a function of a child's RL age in order to yield "language equivalent" norms for speech audiometry. In contrast to performance for PSI sentence materials, performance for PSI word materials was not influenced by differences in RL skill. Reliability coefficients for PSI word and sentence test-retest measures ranged from about 0.85 to 0.95 in normal-hearing and hearing-impaired children. Illustrative PSI results in children with confirmed central auditory disorders are presented.

Age Factors↗

Interlist equivalency of the CID W-22 word lists presented in quiet and in noise.

The interlist equivalency of the CID W-22 word lists administered in quiet and in a background of noise was investigated using 48 normal-hearing subjects. All four word lists were administered at 20 dB SL in quiet and in the presence of a multitalker babble (0 dB signal-to-noise ratio). In the statistical analyses, word performance and subject performance were used as the dependent measures. The results indicated that: (1) the lists are equivalent when administered in quiet; (2) the lists are not equivalent when administered in a background of multitalker babble; (3) the addition of noise changes the relationship among the word lists in a nonpredictive manner; and (4) the addition of noise changes the level of difficulty of some words of each list to a greater degree, relative to the other words. The results are discussed relative to their implications for hearing evaluation and hearing aid evaluation procedures.

Adult↗

Hearing aid gain and frequency response requirements for the severely/profoundly hearing impaired.

The optimal frequency response slope, from the low frequencies (250 or 500 Hz) to 2000 Hz, was estimated for each of 46 severely or profoundly hearing-impaired adults. The estimates were derived from paired comparison judgments of speech filtered to simulate different frequency response conditions, from home trials and ratings of different tone settings of high-powered, behind-the-ear hearing aids, and for 28 subjects, from speech recognition testing. The estimated optimal response, expressed as the slope from 250 to 2000 Hz and as the slope from 500 to 2000 Hz, was compared with the response prescribed by the National Acoustic Laboratories (NAL) procedure and its relationship to audiometric variables was analyzed. Insertion gain was measured for the preferred volume setting with the best frequency response. Preferred gain was typically about 10 dB higher than the NAL prescribed gain. Considering these results in relation to other data, it appears that the "half-gain" rule ceases to apply when HTL exceeds about 70 dB. The estimated optimal frequency response agreed with the NAL response for some subjects but relatively more low frequencies were required for between a third and half of the subjects, depending upon how frequency response is expressed. Generally, more low frequencies were required if HTL at 2000 Hz exceeded 95 dB, whereas the NAL response was usually appropriate for other cases.

Adult↗

Candidates for multiple frequency response characteristics.

This study examined what types of subjects may benefit from the use of multiple memory hearing aids that offer variation in their frequency response characteristics. Thirty subjects with varied degrees and configurations of hearing loss compared an individually prescribed frequency response (NAL) and two variations in which the real-ear response slope was either increased (more high-frequency emphasis) or decreased by about 3 dB/octave over the range from 500 Hz to 4000 Hz. The evaluations consisted of paired comparison judgments of pleasantness and of ease of understanding speech, in quiet and in three background noises with substantially different acoustic spectra (traffic noise, speech babble, and high-frequency noise). Twelve of the 30 subjects selected different frequency responses for different background noises and/or for different response criteria. These subjects were characterized as having the more severe high-frequency hearing losses (averaged across 2000, 3000, and 4000 Hz). They also tended to be those for whom the three frequency responses provided the greatest variation in real-ear low-frequency gain. (Despite substantial electronic variations, some subjects received only small variations in real-ear gain at the low frequencies). When subjects chose a different response for different conditions, they tended to prefer responses for which the slope was negatively related to the spectrum of the stimulus. This was true for both response criteria. The conclusion is that hearing aid users with substantial high-frequency losses, and who can be fitted with sufficient variation in the low-frequency real-ear gain, have the potential to benefit from having a choice of frequency response characteristics.

Adolescent↗

Central auditory processing in urban black children: a normative study.

A major issue concerning central auditory nervous system (CANS) evaluation is the appropriateness of the norms used. The use of currently available CANS norms in the evaluation of urban black children may result in inaccurate diagnosis. The subjects of this study were 40 black children who were intellectually, functionally, and behaviorally normal. Ages ranged from 7 years 4 months to 11 years 4 months. Candidates were identified by classroom teachers, then evaluated by specialists, using interviews, records, observation, and tests to identify "hidden" handicaps. Performance data were obtained on each of the age groups for the following CANS tests: time compressed speech; competing sentences; filtered speech; binaural fusion; alternating sentences; and staggered spondaic words. The results indicated that the performance of normal black children on the CANS test used in this study is not quantitatively nor qualitatively different from the performance of normal white subjects on the same tests.

Black or African American↗

Effects of hearing loss and spectral shaping on identification and neural response patterns of stop-consonant stimuli.

In order to determine the effects of hearing loss and spectral shaping on a dynamic spectral speech cue, behavioral identification and neural response patterns of stop-consonant stimuli varying along the /b-d-g/ place-of-articulation continuum were measured from 11 young adults (mean age = 27 years) and 10 older adults (mean age = 55.2 years) with normal hearing, and compared to those from 10 older adults (mean age = 61.3 years) with mild-to-moderate hearing impairment. Psychometric functions and N1-P2 cortical evoked responses were obtained using consonant-vowel (CV) stimuli with frequency-independent (unshaped) amplification as well as with frequency-dependent (shaped) amplification that enhanced F2 relative to the rest of the stimulus. Results indicated that behavioral identification and neural response patterns of stop-consonant CVs were affected primarily by aging and secondarily by age-related hearing loss. Further, enhancing the audibility of the F2 transition cue with spectrally shaped amplification partially reduced the effects of age-related hearing loss on categorization ability but not neural response patterns of stop-consonant CVs. These findings suggest that aging affects excitatory and inhibitory processes and may contribute to the perceptual differences of dynamic spectral cues seen in older versus young adults. Additionally, age and age-related hearing loss may have separate influences on neural function.

Acoustic Stimulation↗

The effect of linguistic entropy on speech perception in noise in young and elderly listeners.

The rationale for a method to quantify the information content of linguistic stimuli, i.e., the linguistic entropy, is developed. The method is an adapted version of the letter-guessing procedure originally devised by Shannon [Bell Syst. Tech. J. 30, 50-64 (1951)]. It is applied to sentences included in a widely used test to measure speech-reception thresholds and originally selected to be approximately equally redundant. Results of a first experiment reveal that this method enables one to detect subtle differences between sentences and sentence lists with respect to linguistic entropy. Results of a second experiment show that (1) in young listeners and with the sentences employed, manipulating linguistic entropy can result in an effect on SRT of approximately 4 dB in terms of signal-to-noise ratio; (2) the range of this effect is approximately the same in elderly listeners.

Adult↗

Comparison of different speech processing strategies on patients receiving the same implant.

Two subjects with transcutaneously connected 8-electrode scala tympani implants were given subsets of the Minimal Auditory Capabilities test during stimulation with five speech processing strategies--two single channel and three multichannel. While there were significant (p = 0.05%) scores on some items with all types of stimulation, one subject did as well with single channel analog as with multichannel stimulation. She is an enthusiastic full-time user of single channel stimulation. The other, a nonuser of the same device, preferred (and performed better with) one of multichannel stimulation. This is an interim report because neither subject has yet had the opportunity of nonlaboratory use of the multichannel schemes.

Adult↗

Evaluation of the speech perception in noise (SPIN) test.

Several investigations were perfomed with normal hearing subjects to determine the effects of presentation level and signal-to-babble ratio on the speech perception in noise (SPIN) test. The SPIN test contains sentences that simulate a range of contextual situations encountered in everyday speech communication. Findings from several representative patients with sensorineural hearing loss demonstrate the possible clinical utility of the test to measure the effects of context on speech discrimination.

Acoustic Stimulation↗

Development of speech-audiometric materials for native Spanish-speaking adults.

The lack of valid and reliable Spanish speech audiometry materials constitutes an important clinical problem. Such tests necessitate the construction of appropriate materials. Analysis of English and Spanish literature on speech audiometry led to the identification of guidelines for new test materials in the Spanish language. Test lists were devised, recorded and used to evaluate 10 normal-hearing native Spanish-speaking subjects. The results obtained led to a final set of recorded lists. Boston College Auditory Test lists may be used successfully with Spanish-speaking patients. The current study should provide the impetus and sufficient guidelines upon which speech stimuli in other languages may be constructed.

Adult↗