Recognition performance for four combinations of FM system and hearing aidmicrophone signals in adverse listening conditions

Objective: Children with moderate to severe hearing loss routinely use pers onal frequency modulated (FM) systems in the classroom to improve the signa l to noise ratio of teacher-directed speech with notable success. Attention is now being given to the ability of these children to hear other students via the hearing aid (HA) microphone while using an FM system. As a result, a variety of FM system and HA microphone combinations have been recommende d for classroom use. To date, there are no studies regarding the efficacy o f these FM/HA combinations. The purpose of this study was to evaluate recog nition performance using four FM/HA combinations and to characterize that p erformance for stimuli received primarily through FM system and HA micropho ne transmission. Design: Recognition performance for FM system and HA microphone signals was evaluated for two symmetrical and two asymmetrical FM/HA combinations usin g two commercially available FM systems tone conventional and one FM-preced ence circuit). Eleven children (ages 9 to 12) with moderate to severe senso rineural hearing loss and eight children (ages 10 to 11) with normal hearin g served as subjects. The two symmetrical FM/HA combinations included: 1) b inaural FM system and HA microphone input using the conventional FM system, and 2) binaural FM and HA input using the FM-precedence circuit. The conve ntional FM system was used for the two asymmetrical combinations and includ ed: 1) binaural FM input and monaural HA input, and 2) FM input to one ear and HA input to the other. Stimuli were 33 consonants presented in the form of nonsense syllables. The stimuli were presented through three loudspeake rs representing a teacher and two fellow students in a classroom environmen t. Speech shaped noise was presented through two additional loudspeakers. Results: In general, no statistically significant differences in recognitio n performance were found between any of the FM/HA combinations, Mean recogn ition scores for HA microphone transmission (55%) were significantly poorer than those for FM system transmission (75%). As expected, initial consonan ts were more easily recognized than final consonants via FM: system and HA microphone transmission. However, voiceless consonants were more easily rec ognized than voiced consonants via HA microphone transmission, which was no t predicted on the basis of previous research. Conclusions: These results suggest that a certain amount of flexibility is present when choosing an FM/HA combination. However, recognition performanc e via the HA microphones was consistently poorer than performance via FM tr ansmission. Because relevant material also originates from fellow students (e.g., answering teacher-directed questions), input via the HAs is often as important as information originating from the teacher. The results suggest that attempts to improve performance for signals transmitted through the H A microphones in a classroom setting would benefit children with hearing lo ss.