as audiological outcomes including improved sound localization and speech perception. a consensus statement from the european bilateral pediatric cochlear implant forum also confirmed the importance of bilateral cochlear implantation in children. in adults, new research shows that bilateral implantation can improve quality of life and speech intelligibility in quiet and noise. a 2015 review examined whether ci implantation to treat people with bilateral hearing loss had any effect on tinnitus. this review found the quality of evidence to be poor and the results variable: overall total tinnitus suppression rates for patients who had tinnitus prior to surgery varied from 8% to 45% of people who received ci; decrease of tinnitus was seen in 25% to 72%, of people; for 0% to 36% of the people there was no change; increase of tinnitus occurred in between 0% to 25% of patients; and, in between 0 and 10% of cases, people who did not have tinnitus before the procedure, got it. further research found that the electrical stimulation of the ci is at least partly responsible for the general reduction in symptoms. a 2019 study found that although tinnitus suppression in patients with cis is multifactorial, simply having the ci switched on without any audiological input (while standing alone in a soundproof booth) reduced the symptoms of tinnitus. this would suggest that it is the electrical stimulation that explains the decrease in tinnitus symptoms for many patients, and not only the increased access to sound. a 2015 literature review on the use of ci for people with auditory neuropathy spectrum disorder found that, as of that date, description and diagnosis of the condition was too heterogeneous to make clear claims about whether ci is a safe and effective way to manage it. the data for cochlear implant outcomes in older adults differs. 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, people 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. other studies have shown different outcomes, with some reporting that adults implanted at the age of 65 and older showed audiological and speech discrimination outcomes similar to younger adults. while cochlear implants demonstrate substantial benefit across all age groups, results will depend on cognitive factors that are ultimately highly age dependent. however, studies have documented the benefit of cochlear implants in octogenarians. the effects of aging on central auditory processing abilities are thought to play an important role in impacting an individual's speech perception with a cochlear implant. the lancet reported that untreated hearing loss in adults is the number one modifiable risk factor for dementia. in 2017, a study also reported that adults using a cochlear implant had significantly improved cognitive outcomes including working memory, reaction time, and cognitive flexibility compared to people who were waiting to receive a cochlear implant. prolonged duration of deafness is another factor that is thought to have a negative impact on overall speech understanding outcomes for ci users. however, a 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. a 2016 systematic review of ci for people with unilateral hearing loss (uhl) found that of the studies conducted and published, none were randomized, only one evaluated a control group, and no study was blinded. after eliminating multiple uses of the same subjects, the authors found that 137 people with uhl had received a ci. while acknowledging the weakness of the data, the authors found that ci in people with uhl improves sound localization compared with other treatments in people who lost hearing after they learned to speak; in the one study that examined this, ci did improve sound localization in people with uhl who lost hearing before learning to speak. it appeared to improve speech perception and to reduce tinnitus. in terms of quality of life, several studies have shown that cochlear implants are beneficial in many aspects of quality of life, including communication improvements and positive effects on social, emotional, psychological and physical well-being. a 2017 narrative review also concluded that the quality of life scores of children using cochlear implants were comparable to those of children without hearing loss. studies involving adults of all ages reported significant improvement in qol after implantation when compared to adults with hearing aids. this was often independent of audiological performance. society and culture usage as of october 2010, approximately 188,000 individuals had been fitted with cochlear implants. as of december 2012, the same publication cited approximately 324,000 cochlear implant devices having been surgically implanted. in the u.s., roughly 58,000 devices were implanted in adults and 38,000 in children. as of 2016, the ear foundation in the united kingdom, estimates the number of cochlear implant recipients in the world to be about 600,000. the american cochlear implant alliance estimates that 217,000 people received cis in the united states through the end of 2019. cost and insurance cochlear implantation includes the medical device as well as related services and procedures including pre-operative testing, the surgery, and aftercare that includes audiology and speech language pathology services. these are provided over time by a team of clinicians with specialized training. all of these services, as well as the cochlear implant device and related peripherals, are part of the medical intervention and are typically covered by health insurance in the united states and many areas of the world. these medical services and procedures include candidacy evaluation, hospital services inclusive of supplies and medications used during surgery, surgeon and other physicians such as anesthesiologists, the cochlear implant device and system kit, and programming and (re)habilitation following the surgery. in many countries around the world, the cost of cochlear implantation and aftercare is covered by health insurance. in the usa, as cochlear implants have become more commonplace and accepted as a valuable and cost effective health intervention, insurance coverage has expanded to include private insurance, medicare, tricare, the va system, other federal health plans, and medicaid. in september 2022 the centers for medicare & medicaid services expanded coverage of cochlear implants for appropriate candidates under medicare. candidates must demonstrate limited benefit with appropriately fit hearing aids but with criteria now defined by test scores of less than or equal to 60% correct in the best-aided listening condition on recorded tests of open-set sentence recognition. just as there is with any medical procedure, there are typically co-pays which vary depending upon the insurance plan. in the united kingdom, the nhs covers cochlear implants in full, as does medicare in australia, and the department of health in ireland, seguridad social in spain, sécurité sociale in france and israel, and the ministry of health or acc (depending on the cause of deafness) in new zealand. in germany and austria, the cost is covered by most health insurance organizations. public health 6.1% of the world population live with hearing loss, and it is predicted that by 2050, more than 900 million people around the globe will have a disabling hearing loss. according to a who report, unaddressed hearing loss costs the world 980 billion dollars annually. particularly hard hit are the healthcare and educational sectors, as well as societal costs. 53% of these costs are attributable to low- and middle-income countries. the who reports that cochlear implants have been shown to be a cost-effective way to mitigate the challenges of hearing loss. in a low-to-middle-income setting, every dollar invested in unilateral cochlear implants has a return on investment of 1.46 dollars. this rises to a return on investment of 4.09 dollars in an upper-middle-income setting. a study in colombia assessed the lifetime investments made in 68 children who received cochlear implants at an early age. taking into account the cost of the device and any other medical costs, follow-up, speech therapy, batteries and travel, each child required an average investment of us$99 000 over the course of their life (assuming a life span of 78 years for women and 72 years for men). the study concluded that for every dollar invested in rehabilitation of a child with a cochlear implant, there was a return on investment of us$2.07. manufacturers as of 2021, four cochlear implant devices approved for use in the united states are manufactured by cochlear limited, the advanced bionics division of sonova, med-el, and oticon medical. in europe, africa, asia, south america, and canada, an additional device manufactured by neurelec (later acquired by oticon medical) was available. a device made by nurotron (china) was also available in some parts of the world. each manufacturer has adapted some of the successful innovations of the other companies to its own devices. there is no consensus that any one of these implants is superior to the others. users of all devices report a wide range of performance after implantation. criticism and controversy much of the strongest objection to cochlear implants has come from within the deaf community, some of whom are pre-lingually deaf people whose first language is a sign language. some in the deaf community call cochlear implants audist and an affront to their culture, which, as they view it, is a minority threatened by the hearing majority. this is an old problem for the deaf community, going back as far as the 18th century with the argument of manualism vs. oralism. this is consistent with medicalisation and the standardisation of the "normal" body in the 19th century when differences between normal and abnormal began to be debated. it is important to consider the sociocultural context, particularly in regards to the deaf community, which has its own unique language and culture. this accounts for the cochlear implant being seen as an affront to their culture, as many do not believe that deafness is something that needs to be cured. however, it has also been argued that this does not necessarily have to be the case: the cochlear implant can act as a tool deaf people can use to access the "hearing world" without losing their deaf identity. cochlear implants for congenitally deaf children are most effective when implanted at a young age. evidence shows that deaf children of deaf parents (or with fluent signers as daily caregivers) learn signed language as effectively as hearing peers. some deaf-community advocates recommend that all deaf children should learn sign language from birth, but more than 90% of deaf children are born to hearing parents. since it takes years to become fluent in sign language, deaf children who grow up without amplification such as hearing aids or cochlear implants will not have daily access to fluent language models in households without fluent signers. critics of cochlear implants from deaf cultures also assert that the cochlear implant and the subsequent therapy often become the focus of the child's identity at the expense of language acquisition and ease of communication in sign language and deaf identity. they believe that measuring a child's success only by their mastery of speech will lead to a poor self-image as "disabled" (because the implants do not produce normal hearing) rather than having the healthy self-concept of a proudly deaf person. however, these assertions are not supported by research. the first children to receive cochlear implants as infants are only in their 20s (as of 2020), and anecdotal evidence points to a high level of satisfaction in this cohort, most of whom don't consider their deafness their primary identity. children with cochlear implants are most likely to be educated with listening and spoken language, without sign language and are often not educated with other deaf children who use sign language. cochlear implants have been one of the technological and social factors implicated in the decline of sign languages in the developed world. some deaf activists have labeled the widespread implantation of children as a cultural genocide. as the trend for cochlear implants in children grows, deaf-community advocates have tried to counter the "either or" formulation of oralism vs. manualism with a "both and" or "bilingual-bicultural" approach; some schools are