In his presentation, Harvey Dillon, Ph.D., Research Director of the National Acoustic Laboratories (NAL) in Sydney, Australia, discussed COSI and NAL-NL1, two commonly used tools for individually determining client needs, goals, and amplification requirements. The Client Oriented Scale of Improvement (COSI) assists in the management of motivation, expectations and adjustment to amplification. The NAL-NL1 selection procedure aims to provide the response shape that maximizes speech intelligibility in multi-channel instruments while ensuring that the total loudness is no more than that perceived by a normal-hearing person.

In order to gain insight into the effect COSI had on practitioners and to develop better outcome measures in the future, Dr. Dillon and his colleagues at the National Acoustic Laboratories surveyed professionals utilizing COSI and other outcome measures. The goal was to determine if clinicians liked using outcome tools, and what they found the benefits and drawbacks of COSI to be.

The overall opinion was that COSI reflects good clinical practice and enhances rehabilitation. To most survey participants, COSI was seen as a positive tool providing extra support and information. A smaller number viewed COSI as a time-consuming exercise that duplicated what they were already doing as part of the hearing rehabilitation process.

An interesting finding of the survey, however, was what professionals defined as the applications of COSI. "COSI is an outcome measure," explained Dillon, "but when we did our survey, somewhat to our surprise many of the positive comments had nothing to do with outcomes." Other applications identified by clinicians were assessing acceptance, motivation and expectations; selecting hearing aid devices and features; teaching hearing strategies; and facilitating rapport and concern.

NAL-NL1

One of the important factors that became clear in the creation of NAL-NL1, explained Dr. Dillon, is that when loss gets too great at any frequency, patients cannot utilize information at that frequency as well as people with less hearing loss. Even when speech is amplified to well above hearing threshold, their ability to extract information is greatly reduced compared to people with less loss. For low sensation levels, however, (i.e. speech just a bit above the patient’s threshold), even people with severe loss do almost as well, and in some cases better, than a normal hearing person. In these cases, more is not always better since adding more speech information often does not produce more intelligibility, and can produce less intelligibility.

Other researchers at NAL (Dr. Gitte Keidser and Frances Grant) recently undertook research both in the field and in the laboratory to evaluate the effectiveness of NAL-NL1 as a procedure in comparison with loudness normalization.

Subjective preferences, and measured speech intelligibility both strongly favoured the NAL-NL1 method over loudness normalization, especially when listening in background noise, even though both procedures were rated as being equally loud in the laboratory. Common comments by the subjects after the field test component were that NAL-NL1 makes speech clearer, and is more natural while loudness normalization sounds soft, muffled, and dull. In high-level noise situations in the field, NAL-NL1 was rated as being louder and sometimes less comfortable. Some differences were noted between patients with flat losses and those with sloping losses.

The studies also looked at whether multi-channel hearing devices were preferred. In terms of speech recognition in the laboratory, there were few significant differences in user preference or objective performance between one-, two-, and four-channel devices. Dr. Dillon noted that this was a surprising result and one that required further investigation. In the field-study phase, those subjects with steeply sloping losses preferred the two-channel device over the single-channel device. (The four-channel device was not used in the field study).

Overall, the experiment supported the use of NAL-NL1 and indicated that the number of channels in the hearing aid was not a critical issue.

To view the PowerPoint presentation, click here.