A 2016 research study found that age at implantation was highly correlated with post-operative speech understanding performance for various test measures. In this study, patients who were implanted at age 65 or older performed significantly worse on speech perception testing in quiet and in noisy conditions compared to younger CI users. The deleterious effects of aging on central auditory processing abilities are thought to play an important role in impacting an individual's speech perception abilities with CI. Prolonged duration of deafness is another factor which is thought to have a negative impact on overall speech understanding outcomes for CI users. However, this particular study found no statistical difference in the speech understanding abilities of CI patients over 65 who had been hearing impaired for 30 years or more prior to implantation. In general, outcomes for CI patients are dependent upon the individual's level of motivation, expectations, exposure to speech stimuli and consistent participation in aural rehabilitation programs.