The report was discussed with representatives of hearing-aid groups, wireless service providers and manufacturers, hearing-aid manufacturers and the Federal Communications Commission.

"This study is the first major, comprehensive scientific effort in the United States that involves a large group of people with hearing aids," said Hank Grant, Chairman of the Board of Directors of the Oklahoma Center. "The key objective is to evaluate sh ort-term and long-term solutions that will enable people with hearing aids to use the new digital wireless phones."

When completed, the study will have evaluated most North American digital phone technologies. To date, studies are underway with 1900 MHz PCS (J007), 800 MHz TDMA (IS-54) and 800 MHz CDMA (IS-95).

Phase I of the Hearing Aid Project is to conduct testing with hearing aid users in order to (i) determine the existence and severity of the interference as a function of hearing aid type, wireless phone technology and hearing loss configuration, and (ii) evaluate the effectiveness of proposed solutions. The study is being conducted in cooperation with the Hough Ear Institute in Oklahoma City. Phase II of the Hearing Aid Project will involve instrument-based testing with an emphasis on identifying the mech anism of the interaction and leading to the development and evaluation of longer term solutions.

The clinical trials with hearing aid users (Phase I) began in late December 1995. "Because only 18 of the 75 people involved with the study have been tested, conclusions are premature at this time," said Ravi Ravindran, Project Director of the Oklahoma Ce nter.

However, the research has yielded these observations:

• The first three digital phone technologies examined some degree of interference with the hearing aids that have been tested.
  
• Testing to date has not yet characterized the extent of interference for different phone technologies and types of hearing aids because of the limited sample size.
  
• Shielding of phones and hearing aids helped reduce interference. The feasibility of shielding and other interference mitigating techniques will be pursued.
  
• Among the different types of hearing aids, Behind-The-Ear (BTE) units have demonstrated the most significant interaction. This is consistent with the results from other similar studies.

Phase I results were presented on April 29, 1996 to representives of hearing aid user groups, wireless service providers and manufacturers, hearing aid manufacturers and the Federal Communications Commission.

"This clinical study is the most comprehensive scientific effort to date in the United States to involve a diverse group of hearing aid users to determine the degree of interaction between hearing aids and wireless phones," said Ravi Ravindran, Director o f the Oklahoma EMC Center. "This study has identified several factors that contribute to the interaction and also demonstrated the complexity of the problem."

Phase I research focused on evaluating worst-case interaction conditions for hearing aid and phone technologies. Phase II of the Hearing Aid Project will involve both instrument-based and hearing aid user testing with an emphasis on identifying the mechan ism of the interaction and leading to the development of standards for hearing aid immunity and phone emissions, and the evaluation of solutions. When completed, the study will have evaluated most North American digital phone technologies. To date, studie s involving hearing aid users have been completed with 1900 MHz PCS (J007), 800 MHz TDMA (IS-54) and 800 MHz CDMA (IS-95), where the numbers in parentheses refer to particular industry standards for modulation schemes.

The Hearing Aid study is being conducted by the University of Oklahoma Wireless EMC Center in cooperation with the Hough Ear Institute in Oklahoma City. The clinical trials with hearing aid users (Phase I) began in December 1995. Seventy-eight people (68 hearing aid users and 10 non-hearing aid users) were tested by the end of March 1996. "A statistical analysis of the clinical data was performed to determine the degree of interaction as a function of hearing aid type, hearing loss configuration, selected wireless phone technology and the severity of the hearing loss," said Robert Schlegel, a lead researcher in the project. "The clinical trials also included the investigation of some proposed solutions to minimize the interaction."

Two interference measures - speech recognition (words identified correctly from a standard audio-taped word list) and annoyance ratings (0-5 scale; 0-no interference to 5-unbearable) were used to determine the degree of interaction when hea ring aid wearers use a digital phone at a 2cm distance (less than 1 inch). Two additional measures were used to determine the interference to a hearing aid wearer due to passer-by use of a wireless phone - detection threshold (the distance at whic h a hearing aid user detects interference, not necessarily annoying) and annoyance ratings at fixed distances between 25 and 300 cm (10 inches to 10 feet).

The phones were tested in their worst-case interference mode (at their highest operating power) so as to determine the maximum potential interference, realizing that phones operate at varying power levels, all of which are less severe as an interferen ce source compared to full-power operations. Caution must be exercised in using these results to directly contrast one phone technology with another, due to differences in the frequency bands used and differences in the implementation of these technologie s. Hence, the results should be interpreted appropriately.

The followinig general conclusions can be drawn from the Phase I results:

1.The three phone technologies tested (J007-PCS1900; IS54-TDMA800; IS95-CDMA800) interfere in some instances, but not all, with hearing aids with respect to all four interference measures - speech recognition, annoyance rating at 2 cm, passer-by detection threshold, and passer-by annoyance rating (25-300 cm).

2.Analog cellular phone tests did not produce any interference.

3.Non-hearing aid users responded in a very different fashion from hearing aid users in the speech recognition and annoyance tests. Hence, their use as test subjects is inappropriate in examining hearing aid interference, developing standards, and evaluat ing solutions.

4.The following factors have been found to generate statistically reliable differences in interference:

• Phone technology
  
• Hearing aid type (behind-the-ear (BTE), in-the-ear full shell (ITE), in-the-ear half shell(HS), in-the-canal(ITC), and completely-in-the-canal(CIC))
  
• Hearing loss configuration(Flat, Sloping,Ski-slope, Rising)
  
• Severity of hearing loss (Mild, Moderate, Moderately Severe, Severe, Profound)

5.The average threshold distance when a hearing aid user perceived any interference (not necessarily annoying) was less than one meter (3.3 feet) between the hearing aid and the wireless phone.

6.On the average, hearing aid users did not experience annoying interference unless the phones were within two feet of the hearing aid. However, the results varied by hearing aid type, hearing loss configuration and severity of hearing loss.

7.Among the three phone technologies tested in the maximum interference configuration, (i.e., full power which is not typical of their operation in normal use) CDMA phones (IS-95) resulted in lower interference across all measures.

8.Among hearing aid types, BTE users experienced the most interference, while ITC users experienced the least. The difference between BTE and ITC interference was statistically reliable.

9.Among hearing loss configurations, ski-slope hearing loss participants experienced the least interference from RF signals.

10.Interference increased with an increase in hearing loss severity.

11.In addition to the factors identified in conclusion 4, the following interaction (combination) effects were also statistically significant:

• Phone technology and hearing aid type
  
• Hearing Loss configuration and hearing aid type
  
For example, participants with BTE hearing aids noticed more interference from PCS-1900(J007) phone signals. CIC users noticed more interference from TDMA-800 (IS-54)phone signals.

12.Shielding the BTE hearing aids with internal or external metallic coating effectively reduced by-stander interference at all distances.

13.Placing a metal shield between the phone antenna and the hearing aid reduced interference. The technical feasibility and manufacturability of any shielding and its impact on phone and system performance have not been evaluated.

"The Phase I research has clearly demonstrated that hearing aid - wireless phone interactions are very complex," said Hank Grant, Chairman of the Board of Directors of the Oklahoma Center. "This study has identified areas for further investigation to deve lop short-term and long-term solutions that will enable people with hearing aids to use the new digital phones." Phase II of the Hearing Aid project has already begun and is expected to be completed by the end of the year.