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Biomedical subjects

H Levitt

Publications and source records attributed to H Levitt.

At least 19 recordsLinked to original sources
PubMed1992

Computer-assisted tracking simulation (CATS).

The tracking technique involves a sender reading consecutive segments from a story and a receiver attempting to repeat each segment verbatim. The reliability and validity of the tracking procedure have been criticized based upon uncontrolled variables such as sender, receiver, and text characteristics. To address these problems, a computer-assisted interactive tracking simulation (CATS) system has been developed in which story segments are presented to the receiver via a video laser disc system and repair strategies are implemented through a computer program.

Communication Devices for People with Disabilities↗
PubMed1992

Speech recognition performance on a modified nonsense syllable test.

A modification of the City University of New York nonsense syllable test (CUNY NST) has been developed in which (a) the several subtests of the original test are replaced with a 22-item consonant-vowel (CV) subtest and a 16-item vowel-consonant (VC) subtest; and, (b) the response choices for each target syllable include all 22 initial and all 16 final consonants, respectively. In addition, the test tokens are presented as isolated syllables without a carrier phrase. These changes enable the resolution of confusions not possible on the original NST, and also the construction of a single confusion matrix each for CVs and VCs, respectively. The modified nonsense syllable test (MNST) provides results that compare favorably to those of the original NST.

Adult↗
PubMed1992

Adaptive procedures for hearing aid prescription and other audiologic applications.

A class of adaptive procedures is described. These procedures are relatively easy to implement and have many useful properties for audiologic applications. Recent advances in programmable hearing aids enable these techniques to be used effectively in adaptive prescriptive fitting of a hearing aid. All of the procedures are based on the simple up-down technique that, in addition to its simplicity, is both efficient and reliable.

Adaptation, Physiological↗
PubMed1991

Simulating reflex induced changes in the acoustic impedance of the ear.

A simple procedure for measuring changes in the acoustic impedance of the ear is described. The technique has several applications, including simulation using a standard coupler of changes in real ear impedance produced by the acoustic reflex. The technique has also been used for calibrating the response time of an otoadmittance meter used in measuring the temporal characteristic of reflex activity.

Acoustic Impedance Tests↗
PubMed1991

Continuous discourse tracking: an analysis of the procedure.

The method of continuous discourse tracking was evaluated in terms of the strategies used by the talker and the types of responses elicited from the listener. Talker utterances were classified into four categories: 1. Complete repetition (of the initial utterance); 2. Partial repetition; 3. Repetition with change in emphasis; and 4. A combined strategy using two or more correction strategies. Listener responses were classified into three categories: 1. Correct repetition of intended utterance; 2. Partially correct repetition; and 3. Totally incorrect repetition or no response. The listeners showed small but statistically significant differences in their response patterns. Much larger differences were observed in the pattern of correction strategies used by the talkers. Differences in correction strategy were also observed between the early and later stages of a talker-listener exchange.

Attention↗
PubMed1991

Paired comparison judgments for hearing aid selection in children.

Three experiments were conducted to investigate the feasibility of using a paired comparison technique to select hearing aids for children. The first two experiments determined the age at which normal-hearing children and hearing-impaired children with mild to moderately severe sensorineural hearing loss could be expected to meet criteria on a paired comparison task involving judgments of auditory clarity. Of 25 normal-hearing children between the ages of 4.0 and 6.4 yr, five out of five children between 6.0 and 6.4 yr of age passed the auditory paired comparison task. Of 10 hearing-impaired children between the ages of 5.5 and 7.4 yr, five out of five children between 6.5 and 7.4 yr of age passed the auditory paired comparison task. In Experiment 3, eight hearing-impaired children between the ages of 5.7 and 7.8 yr judged the clarity of seven hearing aids in two paired comparison, round robin tournaments. The results showed that correlations between the two tournaments were moderate to strong for six children and weak for two children. Of the six children with stronger correlations between tournaments, correlations between paired comparison judgments and phoneme identification scores were moderate to strong for four children and weak for two children. When compared with a hearing aid that approximated a standard prescription, the hearing aid selected by the paired comparison technique neither degraded nor enhanced speech intelligibility. Results from this study indicate that a paired comparison technique is feasible for use with hearing-impaired children 6.5 yr of age, and occasionally younger, who exhibit mild to moderately severe sensorineural hearing loss and are capable of performing the task reliably.

Age Factors↗
PubMed1991

Future directions in signal processing hearing aids.

Digital hearing aids offer many advantages over conventional analog hearing aids, such as programmability, memory, extremely precise, flexible control of electroacoustic characteristics, and advanced signal processing capabilities for noise reduction and speech enhancement. At the present stage of development, digital hearing aids are subject to severe practical constraints with respect to size and power consumption. Hybrid analog/digital hearing aids have been developed which combine some of the advantages of digital technology with the practicality of small, cosmetically acceptable instruments. Recent studies with all-digital and hybrid analog/digital hearing aids have identified trends which are likely to influence future hearing aid design.

Analog-Digital Conversion↗
PubMed1991

Evaluation of orthogonal polynomial compression.

In orthogonal polynomial compression, the short-term speech spectrum is first approximated by a family of orthogonal polynomials. The coefficients of each polynomial, which vary over time, are then adjusted in terms of their average value and range of variation. These adjustments can be used to compress (or expand) temporal variations in the average level, slope, and various forms of curvature of the short-term speech spectrum. The analysis and reconstruction of the short-term speech spectrum using orthogonal polynomials was implemented using a digital master hearing aid. This method of compression was evaluated on eight sensorineurally hearing-impaired listeners. Speech recognition scores were obtained for a range of compression conditions and input levels with and without frequency shaping. The results showed significant advantages over conventional linear amplification when temporal variations in the average level of the short-term spectrum were compressed, a result comparable to that obtained with conventional amplitude compression. A subset of the subjects showed further improvement when temporal variations in spectrum slope were compressed, but these subjects also showed similar improvements when frequency shaping was combined with level-only compression. None of the subjects showed improved speech recognition scores when variations in quadratic curvature were compressed in addition to level and slope compression.

Adult↗
PubMed1991

Signal processing for sensory aids: a unified view.

Sensory aids for hearing impairment have traditionally been categorized according to the modality of stimulation. They can also be categorized according to the degree of speech processing that is used. These two methods of categorization are independent of each other and provide a convenient framework for developing a unified treatment of sensory aids. An advantage of this approach to the categorization and evaluation of sensory aids is that it helps identify fundamental limitations that apply to all sensory aids. For example, many of the constraints limiting the effectiveness of cochlear implants apply equally well to hearing aids, as well as to visual and tactile aids. Two other important factors to be considered in categorizing and evaluating sensory aids are, method of noise reduction and ease of use.

Deafness↗
PubMed1990

Bone vibrator placement and the cancellation technique.

An issue in the measurement of bone conduction sensitivity is the placement of the bone vibrator. The effect of bone vibrator position on the amplitude and phase of the received signal was investigated using a cancellation technique. This technique involves cancelling the signal delivered by the bone vibrator with a signal delivered acoustically via an earphone. At cancellation, the acoustic signal is equal in amplitude but opposite in phase to the bone-conducted signal. Results showed that the amplitude of the received signal did not vary significantly with bone vibrator position close to the center of the forehead whereas the phase of the received signal was critically dependent on bone vibrator position. Substantial intersubject differences were observed in the variation of phase with bone vibrator position. The precision of measurement using the cancellation technique was found to be high.

Acoustics↗
PubMed1990

Studies with digital hearing aids.

Digital hearing aids offer many advantages over conventional hearing aids. These include signal-processing capabilities that are superior to those of a conventional analog hearing aid, methods of signal-processing and control that are unique to digital systems and which cannot be implemented in conventional analog hearing aids, and innovative new techniques that are changing our way of thinking about hearing aids. An example of the first of these advantages is the extremely high precision with which the frequency-gain characteristic can be specified and the use of this capability to study the effects of frequency response irregularities commonly encountered with hearing aids. An example of the second advantage is the use of memory and logical operations in the implementation of multivariate adaptive paired-comparison techniques for more effective hearing-aid prescription. Another example is the use of powerful new signal processing techniques for noise reduction. The third advantage is the most important. The digital hearing aid can be viewed as a generalized hearing instrument which can be used for simulation, testing and prescription, as well as amplification. The use of the digital hearing aid as a simulator of other hearing aids is discussed and an illustrative example provided in which a new form of amplitude compression, orthogonal-polynomial compression, has been simulated using a digital master hearing aid.

Equipment Design↗
PubMed1988

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.

Adult↗
PubMed1988

Recurrent issues underlying the development of tactile sensory aids.

Research in sensory aids has exhibited a cyclic pattern in which periods of great activity, usually initiated by a new discovery or development, are followed by relatively inactive periods. The issues underlying the development of tactile aids are reviewed within this framework.

Cochlear Implants↗
PubMed1987

An evaluation of three adaptive hearing aid selection strategies.

Paired-comparison judgments of intelligibility of speech in noise were obtained from eight hearing-impaired subjects on a large number of hearing aids simulated by a digital master hearing aid. The hearing aids which comprised a 5 X 5 matrix differed systematically in the amount of low-frequency and high-frequency gain provided. A comparison of three adaptive strategies for determining optimum hearing aid frequency-gain characteristics (an iterative round robin, a double elimination tournament, and a modified simplex procedure) revealed convergence on the same or similar hearing aids for most subjects. Analysis revealed that subjects for whom all three procedures converged on the same hearing aid showed a single pronounced peak in the response surface, while a broader peak was evident for the subjects for whom the three procedures identified similar hearing aids. The modified simplex procedure was found to be most efficient and the iterative round robin least efficient.

Adult↗
PubMed1987

Digital hearing aids: a tutorial review.

The basic concepts underlying digital signal processing are reviewed briefly, followed by a short historical account of the development of digital hearing aids. Key problem areas and opportunities are identified, and the various approaches used in attempting to develop a practical digital hearing aid are discussed.

Deafness↗