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Biomedical subjects

R C Bilger

Publications and source records attributed to R C Bilger.

At least 19 recordsLinked to original sources
PubMed2001

A two-microphone dual delay-line approach for extraction of a speech sound in the presence of multiple interferers.

This paper describes algorithms for signal extraction for use as a front-end of telecommunication devices, speech recognition systems, as well as hearing aids that operate in noisy environments. The development was based on some independent, hypothesized theories of the computational mechanics of biological systems in which directional hearing is enabled mainly by binaural processing of interaural directional cues. Our system uses two microphones as input devices and a signal processing method based on the two input channels. The signal processing procedure comprises two major stages: (i) source localization, and (ii) cancellation of noise sources based on knowledge of the locations of all sound sources. The source localization, detailed in our previous paper [Liu et al., J. Acoust. Soc. Am. 108, 1888 (2000)], was based on a well-recognized biological architecture comprising a dual delay-line and a coincidence detection mechanism. This paper focuses on description of the noise cancellation stage. We designed a simple subtraction method which, when strategically employed over the dual delay-line structure in the broadband manner, can effectively cancel multiple interfering sound sources and consequently enhance the desired signal. We obtained an 8-10 dB enhancement for the desired speech in the situations of four talkers in the anechoic acoustic test (or 7-10 dB enhancement in the situations of six talkers in the computer simulation) when all the sounds were equally intense and temporally aligned.

Algorithms↗
PubMed2000

Localization of multiple sound sources with two microphones.

This paper presents a two-microphone technique for localization of multiple sound sources. Its fundamental structure is adopted from a binaural signal-processing scheme employed in biological systems for the localization of sources using interaural time differences (ITD). The two input signals are transformed to the frequency domain and analyzed for coincidences along left/right-channel delay-line pairs. The coincidence information is enhanced by a nonlinear operation followed by a temporal integration. The azimuths of the sound sources are estimated by integrating the coincidence locations across the broadband of frequencies in speech signals (the "direct" method). Further improvement is achieved by using a novel "stencil" filter pattern recognition procedure. This includes coincidences due to phase delays of greater than 2pi, which are generally regarded as ambiguous information. It is demonstrated that the stencil method can greatly enhance localization of lateral sources over the direct method. Also discussed and analyzed are two limitations involved in both methods, namely missed and artifactual sound sources. Anechoic chamber tests as well as computer simulation experiments showed that the signal-processing system generally worked well in detecting the spatial azimuths of four or six simultaneously competing sound sources.

Adult↗
PubMed1998

Psychometric equivalence of recorded spondaic words as test items.

In the determination of the speech-reception threshold (SRT), spondaic words are assumed to be homogeneous with respect to intelligibility; and the assumption of equal intelligibility requires that the words be comparable for all signal levels. Previous attempts to assess the equal intelligibility assumption using word thresholds as the sole criterion are not an adequate basis for specifying the equality of intelligibility. In the present study, the recorded spondaic words (Tillman recording) were analyzed in an attempt to create a more homogeneous set of spondaic words for future laboratory work. To achieve this goal, the data reported by Young, Dudley, and Gunter (1982) and data collected in our laboratory were fitted to a logistic function (psychometric function) from which a 50% point (threshold) and slope were obtained. To specify their acoustical parameters, the recorded spondaic words were digitized and the RMS level and duration of each syllable and word were calculated. None of the RMS or duration measures were correlated with word thresholds, so no attempt was made to equate level or duration. On the other hand, when the threshold of each word was adjusted to equal the mean threshold of the set (n = 36), the dispersion among word thresholds and slopes was greatly reduced. Further, we recommend that small sets of "equally intelligible" spondaic words not be used for clinical testing because set size is a strong factor in determining threshold for spondees (Meyer & Bilger, 1997; Punch & Howard, 1985).

Humans↗
PubMed1997

Effect of set size and method on speech reception thresholds in noise.

OBJECTIVE: The threshold for speech is known to improve as signal (Miller, Heise, & Lichten, 1951) or response (Pollack, 1959) uncertainty is decreased. The definition of threshold as the signal level or signal to noise ratio (S/N) at which a fixed percent-correct score is obtained, therefore, becomes problematic when set size, M, is varied through the range for which threshold varies systematically (M = 2 to M = 16) because the meaning of that fixed percent changes as M is increased or decreased. The goal of the present study is to examine the effect of set size, M, on speech reception thresholds (SRTs) under two testing strategies. DESIGN: SRTs were obtained in the presence of 80 dB SPL white noise for sets containing 2, 4, 8, and 16 words using two different procedures, one in which threshold was based on a fixed percent correct (American Speech-Language-Hearing Association, 1988) and one in which threshold was defined in terms of d' = 1.00. The subjects were 12 young women with normal hearing and little or no experience with audiologic testing procedures. RESULTS: When threshold was based on a fixed percent correct, S/N at threshold was found to be dependent on set size (F = 3.333; df = 3, 33; p = 0.031). When threshold was defined in terms of d' = 1.00, S/N at threshold was found to be independent of set size. CONCLUSIONS: If a smaller set size than that recommended by the American Speech-Language-Hearing Association (1988) guidelines is to be used for obtaining SRTs in a clinical setting, thresholds should be based on a criterion-free measure that is independent of the size of the set of words being tested, if possible.

Adult↗
PubMed1992

Consistent within-session measures of tinnitus.

Two psychophysical methods, a method of adjustment (MOA) and a forced-choice double-staircase adaptive procedure (FCDS) (Jesteadt, 1980), were used to measure the predominant pitch and loudness of tinnitus for 11 subjects during one test session. The FCDS within-session variability of matches to tinnitus pitch was smaller than for the MOA and comparable to the within-session variability obtained when the FCDS procedure was used to match objective stimuli that approximated the frequency and level of the tinnitus. The within-session variability of matches to tinnitus loudness was nearly identical for the FCDS and the MOA and comparable to the within-session variability obtained when the FCDS procedure was used to match objective stimuli that approximated the frequency and level of the tinnitus. For 3 subjects who participated in 20 sessions, the two psychophysical methods produced correlated measures of tinnitus that tracked each other between sessions. This suggests that tinnitus may be stable within a brief time span but fluctuant in the long run.

Adult↗
PubMed1990

Genetic implications of gender differences in the prevalence of spontaneous otoacoustic emissions.

Spontaneous otoacoustic emissions (SOAEs), which occur in about 40% of normal-hearing humans, do not have a firm explanation in auditory theory nor are their distributional properties well understood. To enhance our understanding of SOAEs, we have pooled data from three reports (Hammel, 1983; Strickland, Burns, & Tubis, 1985; Zurek, 1981) to assemble a large enough sample to assess the relevant hypotheses about the effects of ear and gender on their presence. The results, based on loglinear analyses of the pooled sample of 131 normal-hearing subjects, indicated that (a) the prevalence of SOAEs for female subjects [P(S/F) = .533] was significantly higher than that for male subjects [P(S/M) = .268]; (b) the percentage of right ears with SOAEs (36.6%) was significantly greater than that of left ears (25.2%); and (c) right and left ears were not independent with respect to the presence of SOAEs. These results can be explained by assuming that the (a) tendency to exhibit emissions is inherited, perhaps as a sex-linked trait and (b) ears are asymmetric with respect to the anatomical anomalies of the apical portion of the organ of Corti that may precipitate SOAEs.

Adolescent↗
PubMed1989

Adaptation and the masking of tinnitus.

The effect of adaptation on the masking of tinnitus was investigated. Six patients with tinnitus performed two 5-min tracking tasks, each replicated six times. The first task examined the masking of tinnitus by tracking the intensity of a pure tone required to mask the tinnitus. The second task examined adaptation of a suprathreshold tone by tracking the intensity of a pure tone required for constant loudness. For 3 patients, the change required for constant loudness did not differ from the change required for constant maskability. For 3 patients, however, these two changes were different. Possible implications of these results for determining the locus of tinnitus and for the use of tinnitus maskers are discussed.

Adaptation, Physiological↗
PubMed1989

Statistical dependence among the wave latencies of the auditory brain stem response.

If the interpeak intervals in the auditory brain stem response (ABR) are assumed to be statistically independent variables that represent the neural transmission time between loci, then the absolute latency of an ABR wave is the sum of the transmission times between successive loci. Consequently, the correlations between the absolute latencies of the ABR waves would be part-whole correlations whose expected values are appreciably different from r = 0. We derived the expected values of the correlations between the latencies of the ABR waves on the assumption that their latencies are the sum of independent elements (transmission times) and found them to be 0.707, 0.577, and 0.816 for I.III, I.V, and III.V, respectively. In addition, the expected values of the correlations between the latencies of the ABR waves assuming that the absolute wave latencies themselves are independent variables (e.g., rI.III = 0) were derived. Several of the correlations among interpeak and between the interpeak and absolute latencies were demonstrated to be appreciably different from r = 0. It would appear that it is more reasonable to assume that the elements (transmission times) rather than the component latencies are the variables of choice for statistical analysis of ABR data.

Brain Stem↗
PubMed1984

Standardization of a test of speech perception in noise.

All 10 forms of the test of Speech Perception in Noise (SPIN) were presented to 128 listeners who had some degree of sensorineural hearing loss. Presentation of the speech track was at 50 dB above the estimated threshold for the babble track. Signal-to-babble ratio was 8 dB. Half of the subjects listened through headphones and half via loudspeaker. Half were tested in a single session and half in two sessions spaced 2-4 weeks apart. Two markers independently scored every test session. Statistical analyses indicate that transducer, number of visits, and order of test form presentation have little or no effect on test scores, and differences between markers, although significant, are quite small. The subtests consisting of items with strong contextual cues generate an average reliability coefficient of .91, whereas the value for the low-context subtests is .85. The 10 forms do not, however, constitute a set of equivalent forms, and there are large differences in mean performance on the low-context portions.

Adult↗
PubMed1984

Application of theory of signal detection to dichotic listening.

Listener performance during dichotic listening to CV nonsense syllables was assessed with a Yes/No target-monitoring task that provides both hit and false alarm information. The ear advantage was described by a metric, P(C)maxRE - P(C)maxLE, that is relatively insensitive to a listener's criterion or bias toward "yes" or "no" responses. One half of the listeners in two experiments had a significant right-ear advantage. The potential influence of listener criterion on measures of the ear advantage in conventional dichotic listening experiments is discussed.

Adult↗
PubMed1980

Two-tone masking in normal hearing listeners.

Psychophysical measurements of two-tone masking [E. Zwicker, Acustica 4, 415-420 (1954)] were made at 0.25, 0.5, 1, 2, and 4 kHz utilizing a masker level of 62 dB SPL/tone. Fifty-eight "untrained" subjects were tested using a single run of a 4IFC adaptive procedure for each condition. Individual data were highly variable. Average data were systematic; they were analyzed using a two-line-regression procedure and the obtained critical-bandwidth estimates approximated normative values. Analysis of the literature revealed that a substantial increase of estimated critical bandwidth versus masker level occurs in two-tone masking. A portion of this increase appears artificial and stems from the relative effectiveness of the higher frequency masker tone at high masker levels. An alternative masker-frequency spacing is suggested to reduce level effects. Implications for an underlying critical-band mechanism are discussed.

Adolescent↗
PubMed1978

A comparison of the effects of filtering and sensorineural hearing loss on patients of consonant confusions.

It has been found that listeners with sensorineural hearing loss who show similar patterns of consonant confusions also tend to have similar audiometric profiles. The present study determined whether normal listeners, presented with filtered speech, would produce consonant confusions similar to those previously reported for the hearing-impaired listener. Consonant confusion matrices were obtained from eight normal-hearing subjects for four sets of CV and VC nonsense syllables presented under six high-pass and six-low pass filtering conditions. Patterns of consonant confusion for each condition were described using phonological features in sequential information analysis. Severe low-pass filtering produced consonant confusions comparable to those of listeners with high-frequency hearing loss. Severe high-pass filtering gave a result comparable to that of patients with flat or rising audiograms. And, mild filtering resulted in confusion patterns comparable to those of listeners with essentially normal hearing. An explanation in terms of the spectrum, the level of speech, and the configuration of this individual listener's audiogram is given.

Audiometry↗
PubMed1978

Galvanic disruption of vestibulospinal postural control by cochlear implant devices.

All subjects with implanted cochlear stimulators demonstrated evidence of abnormal postural stability without their stimulators activated. Instability increased when they were tested with cochlear stimulation units turned on, and additional instability was demonstrated in four of these subjects when tested in noise. These findings suggest that the electrical stimulation delivered by the cochlear prosthesis is not limited to the auditory system. The precise characteristics of electrical stimulation devices designed for stimulations limited to the cochlea and their spurious effects upon motor performance should be investigated. The design of future intralabyrinthine auditory electrical prostheses must include hardware designs and stimulus paradigms that avoid undesirable vestibular system stimulation.

Adult↗
PubMed1976

Temporal acuity in listeners with sensorineural hearing loss.

Temporal acuity, the minimum time interval within which the auditory system can discriminate the order of auditory events, was measured for three listeners with normal hearing and for 10 listeners with sensorineural hearing loss. Eight of the 10 listeners with sensorineural loss showed better temporal acuity for conditions with greater loss. The remaining two listeners showed the opposite effect. The temporal acuity results are not well correlated with either speech discrimination scores or measures of recruitment. The temporal acuity results do appear to be correlated with results observed in studies of temporal integration or brief-tone audiometry. Listeners with sensorineural loss tend to have both poor temporal integration and good temporal acuity. This suggests that the two temporal measures may reflect a single time constant in the auditory system.

Adult↗
PubMed1976

Consonant confusions in patients with sensorineural hearing loss.

Consonant confusion matrices were obtained from 22 outpatient listeners with sensorineural hearing loss for four sets of CV and VC nonsense syllables, presented monaurally at SRT + 40 DB. Testing was typically conducted for six hours on each of two separate days. Overall performance and patterns of confusions were stable over time. Analysis of the matrices in terms of phonological features indicated that the patterns of consonant confusions varied both with degree and configuration of the subject's loss. Scaling of intersubject similarity using a pairwise multidimensional scaling analysis resulted in consistent classification of subjects according to audiometric configuration into three groups-essentially normal hearing, flat or rising audiograms, and high-frequency hearing losses.

Adult↗