***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Objective : To determine the efficacy of “ simultaneous ” bilateral cochlear implantation ( both implants placed during a single surgical procedure ) by comparing bilateral and unilateral implant use in a large number of adult subjects tested at multiple sites . Design : Prospect i ve study of 37 adults with postlinguistic onset of bilateral , severe to profound sensorineural hearing loss . Performance with the bilateral cochlear implants , using the same speech processor type and speech processing strategy , was compared with performance using the left implant alone and the right implant alone . Speech underst and ing in quiet ( CNCs and HINT sentences ) and in noise ( BKB-SIN Test ) were evaluated at several postactivation time intervals , with speech presented at 0 ° azimuth , and noise at either 0 ° , 90 ° right , or 90 ° left in the horizontal plane . APHAB question naire data were collected after each subject underwent a 3-wk “ bilateral deprivation ” period , during which they wore only the speech processor that produced the best score during unilateral testing , and also after a period of listening again with the bilateral implants . Results : By 6-mo postactivation , a significant advantage for speech underst and ing in quiet was found in the bilateral listening mode compared with either unilateral listening modes . For speech underst and ing in noise , the largest and most robust bilateral benefit was when the subject was able to take advantage of the head shadow effect ; i.e. , results were significantly better for bilateral listening compared with the unilateral condition when the ear opposite to the side of the noise was added to create the bilateral condition . This bilateral benefit was seen on at least one of the two unilateral ear comparisons for nearly all ( 32/34 ) subjects . Bilateral benefit was also found for a few subjects in spatial configurations that evaluated binaural redundancy and binaural squelch effects . A subgroup of subjects who had asymmetrical unilateral implant performances were , overall , similar in performance to subjects with symmetrical hearing . The question naire data indicated that bilateral users perceive their own performance to be better with bilateral cochlear implants than when using a single device . Conclusions : Findings with a large patient group are in agreement with previous reports on smaller groups , showing that , overall , bilateral implantation offers the majority of patients advantages when listening in simulated adverse conditions Objective : Compare results of cochlear implantation in younger and older adults in the domains of disability and h and icap , as well as in tests of word recognition and localization , across unilateral implant ( CI ) , bilateral ( CI + CI ) , and CI with an acoustic hearing aid in the nonimplanted ear ( CI + HA ) . Design : Three parts : retrospective ( postimplant only ) analysis ; prospect i ve ( preimplant versus postimplant ) ; correlation between age and benefit from CI versus CI + CI .  Two age groups , older and younger than 60 years , for the first 2 analyses ; age is a continuous variable for the third analysis . Setting : Tertiary referral hospital clinic . Patients : Postlingually severely-to-profoundly hearing-impaired adults : Totals of 68 CI , 36 CI + CI , and 38 CI + HA in the retrospective part of the study ; totals of 30 CI , 18 CI + CI , and 16 CI + HA in the prospect i ve parts . Numbers vary from these totals on individual measures . Interventions : Patients receive either 1 or 2 cochlear implants ; some with 1 CI opt to retain a hearing aid in the nonimplanted ear . Outcome Measures : Principal measures : Hearing H and icap Inventory for the Elderly , Hearing H and icap Question naire , Speech , Spatial and Qualities of Hearing Scale , word recognition test , and soundfield localization test . The study is exploratory , but proceeding from a null hypothesis of no expected contrast as a function of patient age . Results : All patient groups show significant benefit after implantation . No significant age-related differences are observed in patients with unilateral implant , nor in CI + HA group . In the CI + CI group , the younger cohort showed very substantial increases in both performance and self-rated abilities ; the older cohort provides more mixed outcomes . Conclusion : Results for the CI group confirm and extend earlier research . The result for the younger group of CI + CI patients demonstrates the consistent incremental benefit obtained from a bilateral procedure . The mixed outcome observed in the older CI + CI group might be due to individual differences in interaction between effects of aging and the ability to integrate binaural cues Adult users of unilateral Nucleus CI24 cochlear implants with the SPEAK processing strategy were r and omised either to receive a second identical implant in the contralateral ear immediately , or to wait 12 months while they acted as controls for late-emerging benefits of the first implant . Twenty four subjects , twelve from each group , completed the study . Receipt of a second implant led to improvements in self-reported abilities in spatial hearing , quality of hearing , and hearing for speech , but to generally non-significant changes in measures of quality of life . Multivariate analyses showed that positive changes in quality of life were associated with improvements in hearing , but were offset by negative changes associated with worsening tinnitus . Even in a best-case scenario , in which no worsening of tinnitus was assumed to occur , the gain in quality of life was too small to achieve an acceptable cost-effectiveness ratio . The most promising strategies for improving the cost-effectiveness of bilateral implantation are to increase effectiveness through enhanced signal processing in binaural processors , and to reduce the cost of implant hardware Objective : Preliminary studies show that bilateral cochlear implantation improves speech-recognition ability in many subjects ; however , the magnitude of this improvement has been variable . The objective of our research was to explore means to better differentiate the binaural benefit that many patients who receive bilateral cochlear implants ( CIs )  describe . Hypothesis : Binaural improvements in speech-perception performance will be consistently evident across patients when they are tested in more challenging listening situations . Design : This was a prospect i ve clinical study . Speech-perception performance was compared between the unilateral and bilateral cochlear implant conditions . Because the purpose was to investigate testing parameters that would demonstrate binaural benefit , word- and sentence-recognition tests were administered under several stimulation conditions : with and without noise and at three presentation levels . In addition , all subjects completed the Abbreviated Profile of Hearing Aid Benefit as a measure of subjective benefit . Subjects were adult cochlear implant recipients . Three device manufacturers were represented ( Advanced Bionics Corporation , Cochlear Americas , and the Med-El Corporation ) ; three patients received simultaneous implantation , and the other four patients received sequential CIs . The setting was a comprehensive cochlear implant program/tertiary referral center . The main outcomes measures were speech-recognition scores in percent correct , mean score difference for unilateral versus bilateral conditions , and subjective benefit scores . Results : The most significant improvements in  binaural cochlear implant use were found when subjects were tested with sentence material presented at 60 dB SPL with a + 8 dB signal-to-noise ratio . Six of seven subjects showed significant binaural improvement , with a mean improvement score of 12.43 % ( SD = 5.32 ) . All subjects preferred the binaural listening condition . Measured improvements in quality of life were seen . Conclusions : Preliminary study findings suggest that significant cochlear implant binaural benefit in speech perception may be observed when testing in more difficult listening situations ( i.e. , lower presentation levels and in noise ) . According to the outcome of our study , testing the binaural benefit of CIs requires consideration of suitable test material s and stimulation parameters Objective : The purpose of this 4-year longitudinal study was to assess the stability of the binaural benefits of head shadow , summation , and squelch for bilateral cochlear implant recipients and to quantify these benefits for the underst and ing of speech in noise . Design : This is a prospect i ve study of 9 patients who received simultaneous bilateral insertion of MED-EL COMBI + 40 cochlear implants in a single-stage operation at the University of North Carolina , Chapel Hill , NC . Each patient had postlingual deafness of short duration before insertion of the device . Each year , the patients were tested for word recognition using consonant-nucleus-consonant words in quiet and speech perception in noise using City University of New York sentences . These tests were administered using direct audio input to the implants . Head-related transfer functions were used to simulate speech in noise testing in a spatial environment . Speech was always presented at midline ( 0 ° ) , and the noise masker was presented at either side or midline ( −90 , 0 , + 90 degrees ) . Results : The binaural benefits of head shadow and summation effects developed early in the postoperative period and remained stable throughout the follow-up period . Squelch developed more slowly and was first demonstrated at 12 months after implantation but continued to increase beyond the first year of follow-up . Conclusion : Benefits of head shadow and summation emerge early and remain stable . However , squelch has the most protracted period of development , with increasing benefit after a year or more of implant experience . These data support the idea that binaural integration continues several years after insertion of bilateral cochlear implant devices The Scottish Intercollegiate Guidelines Network ( SIGN ) develops evidence based clinical guidelines for the NHS in Scotl and . The key elements of the methodology are ( a ) that guidelines are developed by multidisciplinary groups ; ( b ) they are based on a systematic review of the scientific evidence ; and ( c ) recommendations are explicitly linked to the supporting evidence and grade d according to the strength of that evidence . Until recently , the system for grading guideline recommendations was based on the work of the US Agency for Healthcare Research and Quality ( formerly the Agency for Health Care Policy and Research ) . 1 2 However , experience over more than five years of guideline development led to a growing awareness of this system 's weaknesses . Firstly , the grading system was design ed largely for application to questions of effectiveness , where r and omised controlled trials are accepted as the most robust study design with the least risk of bias in the results . However , in many areas of medical practice r and omised trials may not be practical or ethical to undertake ; and for many questions other types of study design may provide the best evidence . Secondly , guideline development groups often fail to take adequate account of the method ological quality of individual studies and the overall picture presented by a body of evidence rather than individual studies or they fail to apply sufficient judgment to the overall strength of the evidence base and its applicability to the target population of the guideline . Thirdly , guideline users are often not clear about the implication s of the grading system . They misinterpret the grade of recommendation as relating to its importance , rather than to the strength of the supporting evidence , and may therefore fail to give due weight to low grade recommendations . # # # # Summary points A revised system of determining levels of evidence and grade s Objective : To evaluate the benefits of bilateral electrical stimulation for hearing-impaired adult subjects using the Nucleus 24 cochlear implant in a multicenter study , and to compare and quantify performance on speech perception measures in quiet and in noise and localization ability for unilateral and bilateral cochlear implant use . Design : Repeated single subject measures were carried out for each subject , with each subject serving as their own control . Assessment of unilateral and bilateral listening conditions for performance on tests of speech comprehension and sound localization were performed . Speech comprehension measures were performed in quiet at 0 degree azimuth and in the presence of background noise simultaneously presented from the same speaker and spatially separated by 90 degrees , at S+45 ° N45 ° and at S−45 ° N+45 ° . Test material s included Freiburger monosyllabic words , Oldenburger sentences , and the Hochmair-Schulz-Moser sentences . Tests of localization were performed in the horizontal plane with 12 speaker locations 30 degrees apart using a shortened sentence stimulus from the Hochmair-Schulz-Moser sentences at two possible presentation levels of 55 and 70 dB sound pressure level for assessment of directionality . The binaural advantage provided by bilateral stimulation was calculated with respect to each ear separately , classified as either the better or poorer performing ear for each speech material in quiet and in noise test conditions . For localization of sound , the binaural advantage was compared with left and right ears separately . Paired comparisons for performance data in all conditions were carried out by considering measurements for each subject in different conditions as paired observations and applying the Student ’s t test to determine the statistical difference between the data sets . Setting : Tertiary referral centers with a cochlear implant program . Patients : Thirty-seven profoundly hearing-impaired adults were enrolled in the study , 22 simultaneously and 15 sequentially bilaterally implanted . All patients received the Nucleus 24 cochlear implant and used the Nucleus SPrint or ESPrit 3 G speech processor , with the vast majority using the ACE speech coding strategy . Results : For spatially separated speech in noise conditions , an interaural performance advantage for the ear closest to the speech source ( i.e. , with a superior signal to noise ratio ) compared with that for the ear closest to the noise source ( i.e. , with an inferior signal to noise ratio ) is consistently demonstrated regardless of whether it is the better or poorer performing ear closest to the speech signal . This is referred to as a significant binaural head-shadow benefit , result ing in a mean improvement between −10 dB and −11.4 dB in the critical signal to noise ratio required for 50 % speech comprehension for the Olden-burger sentences and a mean improvement in the maximum score of 42 % to 55 % for the ear closest to the speech signal over the ear farthest away for the Hochmair-Schulz-Moser sentences . Bilateral stimulation is always observed to provide a performance advantage over the unilateral listening condition for either ear when ipsilateral to the noise source . In addition , as demonstrated by approximately half the subjects tested in noise with the Hochmair-Schulz-Moser sentences , a performance advantage of bilateral stimulation may be observed over the better ear alone when positioned ipsilateral to the speech signal , which is referred to as a binaural squelch effect . On average , for the group , this result ed in a statistically 
    Output:
    
All studies showed a significant bilateral benefit in localization over unilateral cochlear implantation .
Bilateral cochlear implants were beneficial for speech perception in noise under certain conditions and several self-reported measures .
Most speech perception in quiet outcomes did not show a bilateral benefit .
The current review provides additional evidence in favor of bilateral cochlear implantation , even in complex listening situations