Digit training in noise can improve cochlear implant users' speech understanding in noise

While auditory training in quiet has been shown to improve cochlear implant (CI) users' speech understanding in quiet, it is unclear whether training in noise will benefit speech understanding in noise. The present study investigated whether auditory training could improve CI users' speech recognition in noise and whether training with familiar stimuli in an easy listening task (closed-set digit recognition) would improve recognition of unfamiliar stimuli in a more difficult task (open-set sentence recognition).

CI users' speech understanding in noise was assessed before, during, and after auditory training with a closed-set recognition task (digits identification) in speech babble. Before training was begun, recognition of digits, Hearing in Noise Test (HINT) sentences, and IEEE sentences presented in steady speech-shaped noise or multitalker speech babble was repeatedly measured to establish a stable estimate of baseline performance. After completing baseline measures, participants trained at home on their personal computers using custom software for approximately 30 mins/day, 5 days/wk, for 4 wks, for a total of 10 hrs of training. Participants were trained only to identify random sequences of three digits presented in speech babble, using a closed-set task. During training, the signal-to-noise ratio was adjusted according to subject performance; auditory and visual feedback was provided. Recognition of digits, HINT sentences, and IEEE sentences in steady noise and speech babble was remeasured after the second and fourth week of training. Training was stopped after the fourth week, and subjects returned to the laboratory 1 mo later for follow-up testing to see whether any training benefits had been retained.

Mean results showed that the digit training in babble significantly improved digit recognition in babble (which was trained) and in steady noise (which was not trained). The training benefit generalized to improved HINT and IEEE sentence recognition in both types of noise. Training benefits were largely retained in follow-up measures made 1 mo after training was stopped.

The results demonstrated that auditory training in noise significantly improved CI users' speech performance in noise, and that training with simple stimuli using an easy closed-set listening task improved performance with difficult stimuli and a difficult open-set listening task.