An examination of the practicality of the simplex procedure

Objective: The practical importance of the simplex procedure, a subjective technique used to refine the frequency gain characteristic (FGC) of a heari ng aid according to listener preference, was determined for individual list eners by measuring hearing aid benefit using both laboratory studies and fi eld studies. Design: A digital research hearing aid with two memories was used as the te st hearing aid. The modified simplex procedure was used to select the FGC j udged to yield the best speech clarity in the presence of low-level vent no ise and again in higher-level cafeteria noise by 10 experienced hearing aid users. The FGCs assessed by the listeners varied systematically from The N ational Acoustic Laboratories Revised (NAL-R) response in the amount of low -frequency or high-frequency amplification. The benefit obtained with these two simplex-selected settings was compared with that obtained using the NA L-R FGC, Measures of benefit included speech recognition testing in the lab oratory and ratings of speech intelligibility in the field. In the first fi eld study, the two simplex settings were compared. In the second field stud y, the simplex-selected setting for higher level noise and the NAL-R settin g were compared. Results: In the laboratory, the majority of listeners selected an increase in the low-frequency channel gain compared with the NAL-R. Desired high-fre quency channel gain was correlated with degree of hearing loss and type of background noise. The benefit as measured using nonsense syllables did not differ significantly among the three fittings, but differences in benefit w ere measurable with the rating procedure. Five of eight participants notice d a significant difference in their speech understanding in the real world for the FGCs selected in different background noises. Two of seven particip ants reported significantly better speech intelligibility with a simplex-se lected FGC compared with the NAL-R FGC in the real world. The remaining sub jects reported similar speech understanding capabilities with both hearing aid settings. Conclusions: The majority of subjects included in this study selected an FG C with real ear insertion gain different than the NAL-R prescription to imp rove subjective speech understanding in the laboratory, A small number of t hese listeners rated the selected FGC as providing improved speech intellig ibility over the NAL-R FGC in the real world, This finding indicates that t he simplex procedure should be used selectively to modify the NAL-R prescri ption. A screening technique would be useful in selecting those who might b enefit from a modified fitting. The simplex procedure may also prove to be useful in selecting listeners who would benefit from multiple memory hearin g aids.