Use of composite scores (megascores) to measure deficit in amyotrophic lateral sclerosis.

The Tufts Quantitative Neuromuscular Exam (TQNE) consists of 28 items that were designed to measure voluntary motor deficit in amyotrophic lateral sclerosis (ALS) and related diseases. Individual raw data were converted to Z scores for standardization and then grouped into five megascores with statistical and clinical relevance. The derived megascores were Mega 1, pulmonary function; Mega 2, bulbar function; Mega 3, timed hand activities; Mega 4, isometric arm strength; and Mega 5, isometric leg strength. Megascores should enhance the usefulness of testing in therapeutic trials and in analyzing the natural history of ALS and related diseases.

Quantitative assessment of neuromuscular deficit in ALS.

Several criteria must be met in developing a test battery forr ALS. First, the test items should be designed to answer the specific questions being asked. If questions involve the amount and rate of deterioration, then the test items should generate interval data and show evidence that they reflect change in the disease itself. Second, the reliability of the test items should be carefully determined. Are the variances due to testing errors such as inconsistent positioning or changes in verbal instructions; or do they reflect human performance variation? Third, the test items must be sensitive to small changes, and one must be able to test the very strong as well as the severely debilitated patient. The TQNE was designed to measure degree of disease progression in ALS. The major portion of the protocol consists of isometric force measurement using an electronic strain gauge. Other quantitative segments include tests of pulmonary function, speech rates, and timed activities. Using z-score transformations, we have summarized these test items into five megascores: pulmonary function, bulbar function, timed hand activities, arm strength, and leg strength. Megascores have been used to characterize the natural history of the disease and to judge therapeutic efficacy. Quantitative methods to measure deficit in neuromuscular disease lag far behind other technologic advances in medical research. Future advances in the measurement of neuromuscular deficit depend on the commitment of researchers to invest the time and resources necessary to develop more sensitive and reliable testing techniques.

Exploration of factors beyond audibility that may influence speech recognition.

The effects of reduced ability to differentiate acoustic information on speech reception are difficult to separate from the effects of reduced absolute sensitivity. One possible way is to explore abilities to differentiate acoustic information while holding absolute sensitivity constant. Two auditory phenomena known as enhancement and suppression, which are thought to be related to speech reception ability, were evaluated in persons with normal absolute sensitivity who had either normal or reduced speech recognition in noise. Results of forward masking experiments do not support the notion that enhancement or suppression is reduced in persons with reduced speech recognition in noise. However, their pattern of performance differed from that of listeners with normal speech recognition in noise when the duration of certain complex maskers was varied.

Performance of hearing-impaired persons on auditory enhancement tasks.

An auditory enhancement effect was evaluated in normal and hearing-impaired persons using a paradigm similar to that used by Viemeister and Bacon [J. Acoust. Soc. Am. 71, 1502-1507 (1982)]. Thresholds for a 2000-Hz probe were obtained in two forward-masking conditions: (1) the standard condition in which the masker was a four-component harmonic complex including 2000 Hz, and (2) the enhancing condition in which the same harmonic complex except for the exclusion of the 2000-Hz component preceded the four-component masker. In addition, enhancement for speech was evaluated by asking subjects to identify flat-spectrum harmonic complexes that were preceded by inverse vowel spectra. Finally, suppression effects were evaluated by measuring forward-masked thresholds for a 2000-Hz probe as a function of suppressor frequency added to a 2000-Hz masker. Across all subjects, there was evidence of enhancement and better vowel recognition in those persons who also demonstrated evidence of suppression; however, two of the normal-hearing persons demonstrated reduced enhancement yet normal suppression effects.

Evaluation of auditory enhancement and auditory suppression in listeners with normal hearing and reduced speech recognition in noise.

A number of individuals complain of difficulties with speech recognition in noise in spite of normal hearing. This has prompted a search for disruptions in other areas of auditory processing that may account for these deficits. Two processes that may be related to speech recognition, auditory suppression and auditory enhancement, were evaluated in five listeners with normal speech recognition in noise (NSRN) and five listeners with reduced speech recognition in noise (RSRN). Although differences between the two groups were not observed for enhanced forward masking, significant differences were observed in two-tone suppression when the duration of the suppressor was varied. Those with RSRN showed greater suppression than those with NSRN when the suppressor onset preceded the masker onset.

Consistency of electroacoustic characteristics across components of FM systems.

In the absence of national or international electroacoustic standards for the evaluation of Frequency Modulated (FM) amplification systems, it becomes important to know the variability one may expect across similar models. Evaluation of thirty FM systems of the same model obtained from three different educational sites was performed to determine the variability that may occur as a result of the receiver, lapel microphone, or neckloop. There was a range as great as 20 dB in high frequency average saturation sound pressure level and equivalent input noise across receivers, lapel microphones, and neckloops. These results highlight the need for regular electroacoustic monitoring of not only the FM transmitter and receiver, but also the individual components, such as the lapel microphone and the neckloop.

Tone detection and synthetic speech discrimination in band-reject noise by hearing-impaired listeners.

Frequency resolution was evaluated for two normal-hearing and seven hearing-impaired subjects with moderate, flat sensorineural hearing loss by measuring percent correct detection of a 2000-Hz tone as the width of a notch in band-reject noise increased. The level of the tone was fixed for each subject at a criterion performance level in broadband noise. Discrimination of synthetic speech syllables that differed in spectral content in the 2000-Hz region was evaluated as a function of the notch width in the same band-reject noise. Recognition of natural speech consonant/vowel syllables in quiet was also tested; results were analyzed for percent correct performance and relative information transmitted for voicing and place features. In the hearing-impaired subjects, frequency resolution at 2000 Hz was significantly correlated with the discrimination of synthetic speech information in the 2000-Hz region and was not related to the recognition of natural speech nonsense syllables unless (a) the speech stimuli contained the vowel /i/ rather than /a/, and (b) the score reflected information transmitted for place of articulation rather than percent correct.

Self-assessment of communication skills: toward the development of a new speech audiometric tool.

This investigation was carried out in an effort to characterize differences between groups of normal-hearing and hearing-impaired listeners on a speech perception test based on the theory of signal detection (TSD). TSD allows the quantification of two performance measures designed to evaluate listeners' ability to assess the accuracy of their own identifications and their level of confidence in the self-assessment task. It is hoped that these measures will provide a meaningful way to quantify communication skills beyond the percent correct word recognition score routinely measured in the audiology clinic. Nonparametric indices of self-assessment ability and confidence level, P(A) and B, respectively, were measured for ten normal-hearing and ten hearing-impaired subjects at two signal-to-noise ratios (S/N). In addition, percent correct word recognition scores (%C) were measured. Results indicated that %C differed across groups and across S/Ns. In contrast, P(A) and B differed as a function of S/N but did not differ between hearing-impaired and normal-hearing groups.

Vowel identification and vowel masking patterns of hearing-impaired subjects.

Confusion matrices for seven synthetic steady-state vowels were obtained from ten normal and three hearing-impaired subjects. The vowels were identified at greater than 96% accuracy by the normals, and less accurately by the impaired subjects. Shortened versions of selected vowels then were used as maskers, and vowel masking patterns (VMPs) consisting of forward-masked threshold for sinusoidal probes at all vowel masker harmonics were obtained from the impaired subjects and from one normal subject. Vowel-masked probe thresholds were transformed using growth-of-masking functions obtained with flat-spectrum noise. VMPs of the impaired subjects, relative to those of the normal, were characterized by smaller dynamic range, poorer peak resolution, and poorer preservation of the vowel formant structure. These VMP characteristics, however, did not necessarily coincide with inaccurate vowel recognition. Vowel identification appeared to be related primarily to VMP peak frequencies rather than to the levels at the peaks or to between-peak characteristics of the patterns.