A long term effect on speech recognition in the patients with simultaneous bilateral cochlear implants

Abstract

Objective: To investigate an effect on speech recognition after bilateral cochlear implants(CI) simultaneously. Methods: Nine subjects who underwent bilateral CI operation simultaneously in Peking Union Hospital in 2007 were assigned as bilateral group, another 9 subjects with unilateral CI were chosen as unilateral group according to the age, gender, duration of deafness. Hearing threshold, speech recognition of phrases, disyllabic words, single word in quiet and noise environment were calculated, respectively. Three different sound source positions were set up to simulate the three effects of binaural hearing (head shadow, binaural redundancy and binaural squelch) in noise environment. The speech signal intensity was 70 dBSPL, the signal to noise ratio (SNR) was 0 dB, + 4 dB, + 8 dB, and the speech recognition of phrases were examined in bilateral CI group. All the data was analyzed by SPSS 19.0 software. Results: In quiet environment, the average aid-hearing threshold was significantly reduced as (7.2±3.0)dB in bilateral CI group compared to unilateral CI group(P<0.05). However, the speech recognition of phrases, disyllabic words, and single word in quiet and noise environment did not show significant differences between bilateral CI and unilateral CI groups (P>0.05). In the testing under noise environment, the speech recognition of bilateral CI group was significantly higher than that of unilateral CI group (P<0.05). In the estimation of noise environment (SNR=+ 8), the phrase test and speech recognition of head shadow model in bilateral groups were significantly better than that of unilateral group (P<0.01). Further, bilateral CI group showed statistical significances in binaural redundancy and binaural squelch models(P<0.01), there was statistically significant were also found difference between two groups (P<0.01); Bilateral CI group did not reveal significant difference compared with unbilateral CI group in binaural squelch model(P>0.05). Under different signal-to-noise ratio (SNR=+ 8, + 4) noise environment, all the three given models in bilateral CI group show higher signal-to-noise ratio, higher speech recognition rate (Independent-Samples t test, P<0.01). In addition, head shadow model presented negative influences on speech recognition rate compared with binaural redundancy and binaural squelch model by SNR(P<0.05). SNR influences on binaural redundancy and binaural squelch model were almost identical, F=0.371, P=0.549. Conclusion: The subjects who underwent simultaneous bilateral cochlear implantation could significantly reduce aid-hearing threshold, and greatly improve the speech recognition of phrases, disyllabic words, and single word under noise environment.