Middle-ear muscle activity (MEMA) and its association with motor activity in the extremities and head in sleep.

Middle-ear muscle activity (MEMA) in sleep was simultaneously recorded from both ears using extratympanic manometry. Head movement, speech movements, ankle flexion and wrist movement were monitored by electromyographic recording using surface electrodes at the back of the neck, second laryngeal notch, anterior tibialis and forearm muscle. Motor events recorded from these electrode placements were examined for correlation with MEMA to test the hypothesis that the middle-ear muscles are activated in conjunction with other motor activities, aside from eye movements, by a central motor command system. Phi coefficients were calculated for each subject; all were positive, thus indicating an association between MEMA and other noneye movement motor events. These results suggest that there is a central phasic motor system responsible for MEMA and associated phasic motor activity in sleep.

Comodulation masking release and the masking-level difference.

An experiment was performed to determine if the mechanism that mediates comodulation masking release (CMR) is associated with that used to improve detection by the masking-level difference (MLD). The experiment consisted of first improving detectability of a masked diotic tone burst by adding a synchronous noise band at another frequency region (CMR), and then measuring an MLD in the usual manner, by inverting the tone-burst signal to one ear. Results indicate that a substantial MLD can be measured for a signal whose detectability has already been improved by CMR. However, that MLD (9 dB) is smaller than that measured in random noise (14 dB). Put another way, a small CMR (4 dB) can be produced even when the detectability of a stimulus has already been improved due to the MLD. These data are in general agreement with those of Hall et al. [J. Acoust. Soc. Am. 83, 1839-1845 (1988)] and Schooneveldt and Moore [J. Acoust. Soc. Am. 85, 262-272 (1989)].

Speech recognition in analog multichannel cochlear prostheses: initial experiments in controlling classifications.

Computer-synthesized vowels were used to examine methods for controlling and measuring the perceptions elicited during electrical stimulation of the human cochlea. In the first experiment, we measured the importance of the second formant (F2) in the identification of vowels, matched for duration, in a single subject with a multichannel cochlear implant. The subject never confused vowels having a "low" frequency F2 with those having a "high" frequency F2. In the second experiment, identification functions were generated for a series of vowels varying only in F2. When the pattern of F2 stimulation at the basilar membrane was manipulated, vowel identification functions were altered. For the categorization of vowels, the data indicate that the relative cochlear position of F2 stimulation was more important than fine-grain temporal waveform cues. The data are supportive of cochlear implant coding strategies that make use of cochlear place information. In the later experiments, we manipulated filter passbands and channel gains to explore their effect on these classifications. These preliminary studies indicate that it is possible to "fine-tune" such classifications.

The effect of cross-spectrum correlation on the detectability of a noise band.

An experiment was performed to study the interaction of two narrow-band noises having correlated temporal envelopes. The detection threshold of a 100-Hz-wide noise-band signal was measured at different center frequencies in the presence of a continuous 100-Hz-wide noise band having a center frequency of 1000 Hz. The two noise bands had either correlated or independent temporal envelopes. Measured signal detection thresholds are lower when the two noise bands are independent, but the magnitude of this difference is not a simple function of the frequency separation between the two noise bands.

Influence of place synchrony on detection of a sinusoid.

A series of experiments was performed to study the ability of the ear to code the temporal envelope of a waveform as demonstrated by comodulation masking release (CMR). The stimulus for all experiments was composed of a tone-burst signal, a 100-Hz-wide masker band centered at the signal frequency, and a second 100-Hz-wide noise band of variable frequency, the cue band. The cue band had a temporal envelope which was either correlated with or independent of that of the masker. The signal was a 100-Hz tone burst for most experiments. For the monotic stimulus, the correlated cue band results in lowered signal detection thresholds over a range extending from around 2/3 oct below the signal frequency to 1/3 oct above that frequency. When measured dichotically, with the signal and masker band in one ear and the cue band in the opposite ear, that effective range is expanded but the detection threshold shifts are a bit smaller. The greatest CMR is observed when the stimulus is presented diotically. With regard to effects of level and frequency, our data show CMR increasing with increasing stimulus level for a cue band lower in frequency than the signal, but show little effect of level for a cue band higher in frequency. Similarly, CMR increases with increasing stimulus frequency when the cue band is lower in frequency, but shows little effect of frequency for a cue band higher in frequency.

Analysis and revision of the minimal auditory capabilities (MAC) battery.

The Minimal Auditory Capabilities (MAC) Battery was administered individually to 75 hearing aid users with profound sensorineural hearing loss. The purposes of the study were (1) to determine the reliability of the individual tests, their range of difficulty, and their intercorrelations; (2) to undertake a standardization procedure based on data from this population; and (3) to assess the need for revisions. Difficulty ranged gradually from a mean score of 86% correct for the Spondee Same/Different test to a mean of 16% for the NU 6 monosyllabic word test. Alpha estimates of reliability were 0.89 or higher for all but the Everyday Sounds test (0.85), the Question/Statement test (0.83), and the Spondee Same/Different test (0.81). Along with the reliability and range of difficulty results, interest correlations provided no indication that any of the tests should be discarded. In the standardization of the MAC, the mean score correct on each test was set at 100 and the standard deviation at 10. Prepared tables for immediate conversion of a raw score to a standardized score for any test are included in an Appendix. Among revisions, also listed in the Appendix, the CID Everyday Sentences test was reduced to 20 items from 40, the SPIN High-Context Sentences were assigned key words, and the assessment of distinctive feature identification was discontinued.

The revised form of the Hearing Performance Inventory.

The revised Hearing Performance Inventory contains 90 items selected in part on a statistical basis and in part on clinical relevance from a previous experimental form. An analysis of the responses of 354 hearing-impaired subjects was used to evaluate the performance of each of the 90 items remaining in the Revised Form. Because the only items eliminated were either found or deemed to be too easy, too difficult or redundant, the Revised Form maintains the strength of the previous form while reducing significantly the time required for its administration.

Interim assessment of candidates for cochlear implants.

The Minimal Auditory Capabilities battery was administered to patients with profound postlingual sensorineural hearing loss to obtain interim audiometric indices on the relative benefits of cochlear implants and hearing aids. One group used a cochlear implant comprising a multielectrode array and a single-channel stimulator, another group wore hearing aids, with only borderline satisfaction, and the third group wore hearing aids to good advantage. Scores for the latter group were consistently higher than the borderline group on two prosodic tests, but the borderline group scored better on closed-set spondee and vowel recognition tests. Scores were essentially the same for the two groups on the remaining tests. Tentative criteria induces were applied to members of the borderline group in terms of the hearing improvement that might be anticipated from an implant.

Hearing performance inventory.

The Hearing Performance Inventory (HPI) was developed to assess hearing performance in problem areas experienced in everyday listening. It consists of six sections: (1) Understanding Speech, (2) Intensity, (3) Response to Auditory Failure, (4) Social, (5) Personal, and (6) Occupational. A self-report response style is used. Sentences were written to describe a number of listening situations covering a variety of talker characteristics and communication processes. The development, current status, and clinical implications of the HPI are presented.

Development of the California Consonant Test.

A 100-item, multiple-choice test for consonant identification labeled the California Consonant Test (CCT) has been developed expressly for use with hearing-impaired patients. A computer-assisted analysis was obtained for the test responses of 550 patients with sensorineural hearing loss. The test seems highly sensitive to configurations of high-tone loss, but the correlation with degree of loss, especially in the instance of flat configurations, is somewhat low (-0.40). Test-retest correlation is 0.96. A correlation of 0.35 with a W-22 list indicates that the two tests are measuring different aspects of speech reception. In addition to its usefulness in identifying consonant confusions for rehabilitation purposes, the CCT may prove helpful in ranking hearing aids. For the latter purpose, two 50-item subforms, designed for equivalence, have been under observation for possible use when time is a critical factor. Repetitions of the 100-item list offer greater stability, however.

Laser interferometer measurement of changes in crayfish axon diameter concurrent with action potential.

Small rapid changes in the diameter of an axon takes place when an action potential progresses along the axon. In the giant axon of the crayfish these occur within a period of about 1 millisecond and are typically about 18 angstroms in total amplitude.

Binaural masking effects in bone-conducted noise.

When pure tones are masked by bone-conducted noise presented at the midline of the forehead, it is possible that binaural unmasking may occur due to the interaural phase relations of the noise. To study this possibility, the amount of masking produced in bone-conducted noise, in correlated air-conducted noise, and in monaural noise was determined using narrow bands of noise centered at 240, 500, 910, and 1900 Hz as markers and a block up-down two-interval forced choice procedure. The subjects were four women under 30 years of age with 10 dB HTL or better (ANSI, 1969) for the frequencies tested. The amount of unmasking (the masking-level difference) was determined by subtracting the masking levels obtained under each noise condition at each frequency from those obtained in the comparable monaural noise-monaural signal condition. Levels of binaural unmasking obtained in correlated air-conducted noise agreed with those in previously reported experiments. Comparable binaural unmasking effects were demonstrated for midline presentation of bone-conducted noise. Some clinical implications of the findings are discussed.