Real-World Benefit From Directional Microphone Hearing Aids

Subjects- 105 subjects were recruited for participation in this study, thirty-five in each of three hearing loss groups. Subjects were assigned to the three groups according to the severity of their hearing losses. Group 1 (mild) subjects exhibited normal sloping to moderately severe SNHL, with Pure Tone Averages (PTAs) at 500, 1000, and 2000 Hz of less than 35 dB HL. Group 2 (moderate) consisted of subjects with mild sloping to moderately severe SNHL with PTAs of 35 to 50 dB HL. Group 3 (severe) subjects exhibited moderately-severe, sloping to severe-profound SNHL, with PTAs of greater than 50. All subjects had sloping hearing loss defined as at least a 20 dB average difference between 3000 Hz and 500 Hz. (Due to subject drop-out, the final data consisted of 32 subjects in the mild group, 33 in moderate group, and 29 in the severe group)

Hearing status was assessed by means of audiometric pure-tone and speech recognition testing in a group of previous hearing aid users. Normal middle ear function was verified by means of immittance measures. All subjects exhibited absence of significant air-bone gap at any frequency (<10 dB) and normal tympanograms defined as compensated static admittance between 0.25 and 2.5 mmho measured from the positive tail with tympanometric peak pressure between -150 and +100 daPa. All subjects were service-connected veterans who are eligible for care and amplification through the VA Audiology service. All subjects were previous wearers of binaural hearing aids, with a minimum daily usage requirement of 4 hours/day. All subjects were previous users of output compression hearing aids from the same manufacturer.

All subjects participated in approximately eight to ten hours of testing over the course of four visits. At the first visit, subjects received a hearing test, unaided speech understanding in noise measures, and aided speech understanding in noise with their current hearing aids. Additionally, earmold impressions were obtained for the experimental hearing aids. At the second visit, subjects completed the first set of subjective measures for the unaided and current (own) hearing aid conditions. Subjects were then fit with digitally programmable user-selectable directional/omnidirectional hearing aids in the first of two experimental settings (randomly selected between directional/omnidirectional and omnidirectional only), which they used for approximately one month before returning for the next test session. At the third visit, subjects again completed the entire test battery for the experimental hearing aid worn during the last month. The experimental hearing aid was then programmed for the other condition (directional/omnidirectional or omnidirectional only). At the fourth and final visit, subjects completed the entire test battery for this final hearing aid condition. Additionally, at the final visit, subjects completed a preference questionnaire.

Speech understanding in noise tests:

The Connected Sentence Test (CST) and the Hearing In Noise Test (HINT) were administered to all subjects. An investigator in the room with the subject scored the test. The investigator was blinded to the experimental settings of the hearing aids to control for experimenter bias. The CST is a test of speech intelligibility for everyday speech presented at a fixed SNR. The test consisted of 24 pairs of speech passages produced conversationally. The subject's task was to repeat all words of each test sentence. Each passage included 25 key words that were scored correct or incorrect. Subject scores from 1 pair of passages were averaged to obtain an intelligibility score for each experimental condition. Data from Pearsons et al. indicate that real-world SNRs in relatively noisy environments range from approximately +4 dB to -1 dB. Consequently, the tests were administered at a +3 dB SNR, which represented a relatively difficult real-world listening situation. This SNR was chosen to minimize floor and ceiling effects for all subject groups based on a previous investigation in our laboratory, given the steep performance-intensity function that has been reported for the CST.