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Biomedical subjects

B Rakerd

Publications and source records attributed to B Rakerd.

At least 19 recordsLinked to original sources
PubMed2001

Paired-comparison hearing aid preferences: evaluation of an unforced-choice paradigm.

Fifteen normal-hearing listeners compared nine frequency-response slopes in a round-robin paired-comparison tournament as they listened to passages of connected discourse against a competing noise background at a +3-dB signal-to-noise ratio. All participants listened in an AB paradigm, in which they were forced to choose which of two signals (A or B) produced better speech intelligibility, and an ABN paradigm, in which they were allowed a third choice of No Preference (N). For both paradigms, listeners generally preferred frequency shaping that either cut low frequencies or boosted high frequencies, and intra- and intersession reliability was high overall. Although listeners' most-preferred responses tended to converge on the same frequency-response slope in the two paradigms, the reliability of these responses was significantly higher for ABN than for AB. The use of the ABN paired-comparison paradigm deserves further study, therefore, as a method to fit multimemory hearing aids.

Adult↗
PubMed1999

Loudness discrimination of speech signals spectrally shaped by a simulated hearing aid.

A discrimination task was used to assess changes in the loudness of speech that accompanied changes in the spectral tilt of a simulated hearing aid's frequency response. Band-limited (0.25-4 kHz) spondaic words were spectrally shaped at comparison tilt-factor values of -6, 0, and +6 dB per octave and delivered monaurally via insert earphone to each of 10 listeners with normal hearing (NH) and 15 listeners with mild-to-moderate sensorineural hearing impairment (HI). Results for the NH listeners indicated that loudness differences among the tilt factors were generally perceptible and that loudness judgments were highly transitive across different tilt-factor comparisons. Loudness differences were also perceptible to many of the HI listeners when they switched among tilt factors. The HI listeners' data showed some evidence of transitivity, but not so much as was shown by the NH listeners. Intersubject variability in the loudness judgments was found to be comparable for the two subject groups. Results of the study are discussed with regard to their implications for hearing aid fitting, with particular emphasis on the "parameter adjustment and selection" fitting procedure (J. Punch & R. Robb, 1992).

Adult↗
PubMed1999

Identification and localization of sound sources in the median sagittal plane.

The ability of human listeners to identify broadband noises differing in spectral structure was studied for multiple sound-source locations in the median sagittal plane. The purpose of the study was to understand how sound identification is affected by spectral variations caused by directionally dependent head-related transfer functions. It was found that listeners could accurately identify noises with different spectral peaks and valleys when the source location was fixed. Listeners could also identify noises when the source location was roved in the median sagittal plane when the relevant spectral features were at low frequency. Listeners failed to identify noises with roved location when the spectral structure was at high frequency, presumably because the spectral structure was confused with the spectral variations caused by different locations. Parallel experiments on sound localization showed that listeners can localize noises that they cannot identify. The combination of identification and localization experiments leads to the conclusion that listeners cannot compensate for directionally dependent filtering by their own heads when they try to identify sounds.

Adult↗
PubMed1998

On the source-identification method.

The source identification method is a standard psychophysical procedure for studying the ability of listeners to localize the source of a sound. The method can be described in terms of a statistical model in which listeners' responses are determined by the width and bias of an internal distribution. This article presents a theoretical study of the method, particularly the relationships between the average experimental observables, rms error and variability, and parameters of the internal distribution. The theory is tested against source-identification experiments, both easy and difficult. Of particular interest is the experimental dependence of observable statistics on the number of sources in the stimulus array, compared with theoretical predictions. It is found that the model gives a good account of several systematic features seen in the experiments. The model leads to guidelines for the design and analysis of source-identification experiments.

Adult↗
PubMed1998

Sound localization in the median sagittal plane by listeners with presbyacusis.

In Experiment 1, a group of listeners with substantial hearing loss due to presbyacusis and a group of listeners with normal hearing were given three localization tests: a frontal plane test in which they judged whether sounds came from the left, overhead, or the right; a sagittal plane test in which they judged whether sounds came from directly in front, overhead, or behind; and an elevation test in which they judged the vertical position of sounds coming from in front. The two groups performed similarly on the frontal plane test, which chiefly depended upon their ability to use binaural localization cues. They performed differently on the sagittal plane and elevation tests, for which the predominant localization cues were spectral. The listeners with presbyacusis were substantially less accurate than those with normal hearing in both of these instances. They had particular difficulty judging source elevation, rarely scoring much above chance. Follow-up testing of a group of subjects in the early stages of presbyacusis showed localization performance that was intermediate to the other two groups, but far more like that of the normal-hearing listeners. In Experiment 2, additional tests were run with the following conditions designed to encourage improved performance by listeners with presbyacusic hearing loss: (1) filtering of stimuli to preclude masking of more informative high-frequency components by low frequencies; (2) simplification of the elevation test and greater spatial separation of its loudspeaker sources; and (3) use of hearing aids. Conditions 1 and 2 had no appreciable effect on performance; condition 3 significantly improved presbyacusic listeners' ability to localize in the sagittal plane, particularly when sounds came from the front.

Adult↗
PubMed1997

Auditory stimulus intensity and reaction time in listeners with longstanding sensorineural hearing loss.

OBJECTIVE: This study examined relationships among sound level, subjective loudness, and reaction time in listeners with longstanding sensorineural hearing loss and loudness recruitment. DESIGN: A simple reaction-time test was performed by 10 hearing-impaired (HI) subjects with varying degrees of recruitment and by 10 normal-hearing (NH) control subjects. Both groups listened to 0.5 kHz tones presented at a soft level, representing the soft endpoint of a subject's functional dynamic range, and a loud level representing the loud endpoint. In one condition, the loudness level of stimuli within a block was fixed, and hence predictable; in another it varied randomly within a block between loud and soft, adding uncertainty to the simple reaction time task. A test with exactly the same design but using visual stimuli was also performed. RESULTS: 1) In general, the HI subjects responded to auditory stimuli with normal or near-normal mean reaction times when stimulus loudness was predictable. 2) Introduction of uncertainty disrupted the reaction time performance of some, but not all, of the HI subjects. 3) Both the HI and the NH subjects responded more quickly to loud tones than to soft ones. Under the predictable loudness condition the magnitude of this "speed up" was nearly identical for the two groups despite the fact that the HI group had, on average, only half the physical dynamic range of the NH group. 4) Visual reaction-time performance was equivalent between the HI and NH groups in all important respects. CONCLUSIONS: Despite long-term auditory deficits, HI subjects' ability to respond quickly to simple auditory signals is not substantially impaired, particularly when listening under predictable loudness conditions. Although physical soft-loud ranges will generally be narrower than normal for HI subjects, their reaction time performance at the endpoints of that range is likely to be near normal.

Adult↗
PubMed1997

Psychophysical and physiological evidence for a precedence effect in the median sagittal plane.

A listener in a room is exposed to multiple versions of any acoustical event, coming from many different directions in space. The precedence effect is thought to discount the reflected sounds in the computation of location, so that a listener perceives the source near its true location. According to most auditory theories, the precedence effect is mediated by binaural differences. This report presents evidence that the precedence effect operates in the median sagittal plane, where binaural differences are virtually absent and where spectral cues provide information regarding the location of sounds. Parallel studies were conducted in psychophysics by measuring human listeners' performance, and in neurophysiology by measuring responses of single neurons in the inferior colliculus of cats. In both experiments the precedence effect was found to operate similarly in the azimuthal and sagittal planes. It is concluded that precedence is mediated by binaurally based and spectrally based localization cues in the azimuthal and sagittal planes, respectively. Thus, models that attribute the precedence effect entirely to processes that involve binaural differences are no longer viable.

Acoustic Stimulation↗
PubMed1996

Assessing the cognitive demands of speech listening for people with hearing losses.

OBJECTIVE: Measures of listening effort can provide a useful complement to measures of listening performance. The purpose of the present study was to measure the effort required of hearing-impaired subjects when they listen to speech. METHOD: Our subjects performed two tasks simultaneously: a speech task, which took the form of listening to connected discourse; and a digit-memorization task, which competed with the speech task for cognitive resources. Changes in speech-listening effort altered the distribution of resources between the two tasks and modulated memory performance. In two experiments, this dual-task test was given to individuals with congenital/early-onset hearing loss or with presbyacusic hearing loss. We first asked whether they could perform the dual tasks at reasonable levels. If they could, we then asked what their performance revealed about the effortfulness of speech listening, compared with the effort required of normally hearing control subjects. RESULTS: We found the dual-task test to be broadly accessible to hearing-impaired persons. We also found evidence that speech listening was abnormally effortful for both hearing-impaired groups. CONCLUSIONS: These findings encourage further study of attentional and other cognitive factors that accompany speech listening by the hearing impaired.

Adult↗
PubMed1993

Loudness matching of signals spectrally shaped by a simulated hearing aid.

A hearing aid with multiple frequency responses was simulated by programming an equalizer to produce spectral tilt factors of -6, 0, and +6 dB/octave over the frequency range from 0.25 kHz to 4 kHz. Listeners with normal hearing matched the loudness of signals (speech and white noise) that were shaped by these different equalizer settings and delivered via an insert earphone. All signals with spectra that were tilted, either negatively or positively, were perceived as louder than untilted signals. The general pattern of loudness matching was similar across subjects, and intrasubject judgments were found to be highly transitive. A measure of signal power was found to account only moderately well for the individual data. Preliminary evidence from a follow-up study using tilt factors less severe than those used in the main experiment suggests that loudness differences are roughly proportional to the degree of spectral tilt. The incorporation of level corrections approximating those necessary to achieve equal loudness is recommended in the fitting of programmable hearing aids.

Acoustic Stimulation↗
PubMed1993

Auditory spectral discrimination and the localization of clicks in the sagittal plane.

Experiments show that the ability of human listeners to localize an impulsive sound in the medial sagittal plane (front, overhead, rear) deteriorates as the level of the sound increases. This negative level effect is strong for clicks but does not appear for broadband noise. It is conjectured that the negative level effect arises because the tonotopic excitation pattern is broadened for intense impulsive sounds. As a result, the spectral peaks and valleys, which are caused by anatomical filtering and which normally code for localization in the sagittal plane, are less recognizable. Filtered click discrimination experiments using headphones also show a negative level effect for clicks, but not for noise, and support this conjecture.

Acoustic Stimulation↗
PubMed1992

The I' potential of the brain-stem auditory-evoked potential.

We have consistently recorded a positive wave which precedes wave I, and is called I', within the human brain-stem auditory-evoked potential. It is postulated that I' represents initial neural activity of the auditory nerve, which presumably has as its origin auditory nerve dendrites. Thus, I' may represent a summed far-field dendritic potential from currents of excitatory postsynaptic potentials. We report latency and amplitude values of I'.

Acoustic Stimulation↗
PubMed1992

Structural alterations of an ambiguous musical figure: the scale illusion revisited.

The scale illusion (Deutsch, 1975) shows the importance of frequency range in the perceptual organization of a sequence of notes. This paper includes three experiments on the scale illusion. Experiments 1 and 2 demonstrated that if the structure of the pattern of notes used in the original scale illusion study is altered slightly, by adding or subtracting a pair of notes from the ends of the sequence, there is a significant decrease in the rate of frequency-based responses, suggesting a weaker illusion. Experiment 3 investigated two features of the note patterns that may have led to this change. Specifically, it asked whether the decrease in the strength of the illusion is due to (1) the nature of the notes at the extremes of the frequency range and/or (2) the nature of the notes at the crossing point of the two scales. While both sources were found to affect the strength of the scale illusion, the former had a greater influence.

Adult↗
PubMed1989

Localization of sound in rooms. IV: The Franssen effect.

The Franssen effect is an illusion that causes human listeners to make large errors in localizing a sound source. This paper describes steps taken to convert the illusion into an experiment in order to study the localization precedence effect as it operates in rooms. The results of the experiment suggest that there are two components to the illusion: The first is the inability of listeners to localize a sine tone in a room in the absence of an onset; the second is the obscuring of modulation cues by the irregular transient response of a room. Experiments show that the Franssen effect fails completely in an anechoic environment, as expected if the effect depends upon the implausibility of steady-state cues in a room. The Franssen effect also fails when the spectrum of the sound is dense.

Auditory Perception↗
PubMed1989

A microcomputer-based system for auditory evoked potentials.

We have been using a microprocessor/microcomputer-based system which affords flexibility in the recording of neuroaudiologic and neurophysiologic data. To date, we have used it to record auditory sensory and neural events. Data such as spontaneous oto-acoustic emissions, evoked oto-acoustic emissions, compound action potentials, and auditory brain-stem responses can be recorded, displayed and analysed. The system hardware is configured from commercially available and 'off-the-shelf' components. The software which directs stimulus generation, data recording, data display and analysis is all written in compiled BASIC or C. A hard-disk organizational scheme has also been developed to permit ease in categorizing, storing, and using in-house or commercially available systems, utility and applications software.

Computer Systems↗
PubMed1988

Retention of masculine sexual behavior following castration in male B6D2F1 mice.

The reduction of masculine sexual behavior following castration varies widely among genotypes. In contrast to the loss of sexual behavior by castrated males of other strains, males of the B6D2F1 genotype retain the ejaculatory reflex for many weeks after castration. The present study examined this retention phenomenon. Masculine sexual behaviors were measured before and after castration or sham operation in male C57BL/6J, DBA/2J, and B6D2F1 mice. Castrated C57BL/6J and DBA/2J males showed a rapid decline in copulatory behavior. In contrast, 30% of the B6D2F1 males continued to ejaculate 25 weeks after castration. Regardless of whether or not sexual behaviors were retained, levels of plasma testosterone and hypothalamic nuclear estrogen receptors were reduced by castration. These results suggest that the intra- and inter-strain differences in the retention of sexual behavior following castration are not due to differences in levels of steroid hormones. Further, some B6D2F1 males retain the ability to copulate in the absence of gonadal hormone levels required for the maintenance of sexual behavior in other genotypes.

Animals↗
PubMed1987

Domain-final lengthening and foot-level shortening in spoken English.

The literature describes two kinds of durational influence on the syllables of an utterance. They are a lengthening of syllables before many syntactic boundaries ('domain-final lengthening') and a shortening of stressed syllables followed by unstressed syllables ('foot-level shortening'). In the present study we examined the relationship between these two timing phenomena. In particular, we examined the possibility that syntactic boundaries at which lengthening occurs delimit the domains over which foot-level shortening is realized. To test this hypothesis, we varied the syllabic structure of metrical feet spanning word boundaries that either coincided with a noun-phrase (NP)/verb-phrase (VP) boundary or did not. Comparison of stressed syllable durations in these conditions failed to confirm the hypothesis. Instead, unstressed syllables shortened stressed syllables by the same duration across an NP/VP boundary as within a phrase. Our findings suggest that the two effects are independent. The finding that foot-level shortening spans finally-lengthened syntactic boundaries is discussed in relation to theories of the shortening effect.

Humans↗
PubMed1986

Localization of sound in rooms, III: Onset and duration effects.

The steady-state sound field of a sine tone does not provide useful localization information in a room. Nevertheless, listeners can localize a sine tone in a room if it has an onset transient which allows the precedence effect to operate. In the present study, we made a quantitative assessment of onsets and the precedence effect by systematically varying onset duration from 0 s (impulsive), where the precedence effect is maximal, to 5 s, where there is no precedence effect at all. We also assessed listeners' sensitivity to the steady-state sound field under impulsive conditions by varying the total duration of tone pulses. Our experiments were conducted in a room with a single acoustical reflection having various directions and delays, and in an anechoic room. The results for tones of various frequencies (500 and 2000 Hz) and sound-pressure levels (65 and 40 dBA) indicate the following: Localization in rooms is facilitated by onsets even if the onsets are as long as 100 ms. The facilitation depends upon the peak intensity of the tone, as well as the onset duration, suggesting that onset rate is critical for the precedence effect; our results are most consistent with rate expressed as an increase in sound pressure per unit time. The facilitation also depends upon the reflection delay time for a room; gradual onsets take on much more importance for the precedence effect in rooms with long delays. As onsets begin to lose their effectiveness listeners become increasingly "misdirected" by invalid cues in the steady-state sound field. The pattern of misdirection suggests a perceptual averaging of cues over an interval more than an order of magnitude longer than previous estimates of the summation window for the precedence effect. The pattern of misdirection varies with the frequency of a tone, due to frequency-dependent interference effects in a room, but it is independent of signal level. Localization of an impulsive sine tone in rooms is very insensitive to the pulse duration; this suggests that binaural inhibition models of the precedence effect must be supplemented by an evaluative component that we term the "plausibility hypothesis."

Acoustic Stimulation↗