In this paper, head baffle and head shadow effects were measured at a front-oriented and at a back-oriented microphone in a hearing aid casing when worn by human subjects and when placed on a dummy head. Some differences in head baffle and head shadow effects were observed for the front-and back-oriented microphones in that greater head baffle effects were observed at the front microphone than at the back microphone while the reverse was true in terms of head shadow effects. Results obtained with the hearing aid mounted on a dummy head were similar in some respects and in other respects they differed from those observed when the hearing aid was worn by six subjects. Comparison of the results obtained in this study with the data of WIENER measured at the entrance to the ear canal indicated smaller head baffle effects but larger head shadow effects at the hearing aid microphone than at the canal entrance. Finally, it is suggested that reproduction of frequencies above 2 000 HZ and that a resonance peak at about 3 000 HZ in the frequency response curve of a hearing aid may be beneficial to the wearer.

Female↗

PubMedDate not supplied

Masking level differences encountered in clinical populations.

Methods for measuring masking level differences (MLDs) at 500 Hz and for spondees were used with 290 subjects: 50 persons with normal hearing and 240 patients with various diseases. Of particular interest was whether techniques currently in clinical use could be used with ease, dispatch, and profit in determining MLD size. The methods selected, which were variations of Békésy audiometry and speech reception threshold procedures, proved clinically feasible. Results revealed differences in behavior from one group of subjects to another. Although MLDs were not affected by cortical lesions, they were very often abnormally small for patients with eight-nerve tumor, Meniére's disease, or multiple sclerosis. The high incidence of abnormally small MLDs in populations with normal sensitivity to pure tones and speech but with evidence of subcortical central lesions, such as patients with multiple sclerosis, suggests that the MLD tasks can be of diagnostic value in detecting retrocochlear lesions. However, in persons with hearing loss or significant interaural differences in threshold sensitivity, or both, the MLD tests are not always reliable in differentiating cochlear from retrocochlear disease.

Acoustic Stimulation↗

PubMedDate not supplied

Effects of whitening and peak-clipping on speech intelligibility in the presence of a competing message.

The purpose of this experiment was to determine the effects of peak clipping on speech intelligibility when both a target speech and a competing message were simultaneously peak-clipped. A competing message composed of 5 talkers was electrically mixed with CNC discrimination words. This composite signal was presented to normally hearing subjects in three ways: unmodified, whitened, and whitened and peak-clipped. Discrimination functions were obtained for the CNC material by varying the signal-to-competition ratio. Under these conditions, essentially identical discrimination functions were yielded by the unmodified and whitened speech, whereas substantially reduced discrimination scores were obtained with the whitened/clipped speech. These results would suggest that speech intelligibility is reduced by whitening and peak clipping when more than one talker is present. This is true even though earlier studies have shown that whitening and peak clipping do not reduce speech intelligibility when only a single talker is present. Such a finding has implications for wearable amplification.

Acoustic Stimulation↗

PubMedDate not supplied

The intelligibility of whitened and peak clipped speech.

Consonant-nucleus-consonant monosyllabic words were filltered such that each spectral component had equal energy (i.e., "whitened") and peak clipped in one of four ways: minimal, 20, 30, and 40 dB of clipping. In addition, unmodified consonant-nucleus-consonant words were used as stimuli. These different types of sppech were presented to 20 persons with normal hearing at various sensation levels. The results indicate that whitening and peak clipping do not substantially degrade speech intelligibility. In fact, under some conditions whitening and peak clipping may slightly enhance intelligibility.

Adult↗