***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 An aging American population carries a high prevalence of profound sensorineural hearing loss . We examined the performance of multichannel cochlear implant recipients  in a large data base of adult subjects . DESIGN Nonconcurrent prospect i ve study of a national cohort with multivariate regression analysis of preoperative and postoperative performance variables in  multichannel cochlear implant recipients .  We applied models of prediction established in previous studies to the observed results . SETTING Referral centers with active cochlear implant programs . PATIENTS Adolescents and adults with profound hearing loss ( N = 749 ; age range , 14 - 91 years ) . MAIN OUTCOME MEASURE Postoperative monosyllabic word recognition . RESULTS The population 65 years and older demonstrated a clinical ly insignificant 4.6%-smaller postoperative word score compared with the population younger than 65 years . When duration of deafness exceeded 25 years , elderly recipients demonstrated higher word scores than their younger counterparts . A more significant factor affecting outcomes is the ratio of duration of deafness to age at implantation . CONCLUSIONS Age at implantation carried relatively little predictive value for postoperative performance in subjects 65 years and older . Although a small decrement in mean speech recognition scores was evident , the clinical significance of this difference is question able when all of the results observed in elderly patients are considered . A shorter percentage of life spent in severe-to-profound sensorineural hearing loss suggests a foundation of acoustic/auditory processing in the elderly cohort that may mitigate potential physiological effects associated with advanced age . This study confirms and extends previous observations that duration of profound deafness and residual speech recognition carry higher predictive value than the age at which an individual receives an implant PURPOSE The purpose of this study was to examine the rate of progress in the 2nd implanted ear as it relates to the 1st implanted ear and to bilateral performance in adult sequential cochlear implant recipients . In addition , this study aim ed to identify factors that contribute to patient outcomes . METHOD The authors performed a prospect i ve longitudinal study in 21 adults who received bilateral sequential cochlear implants .  Testing occurred at 6 intervals : prebilateral through 12 months postbilateral implantation . Measures evaluated speech recognition in quiet and noise , localization , and perceived benefit . RESULTS Second ear performance was similar to 1st ear performance by 6 months postbilateral implantation . Bilateral performance was generally superior to either ear alone ; however , participants with shorter 2nd ear length of deafness ( < 20 years ) had more rapid early improvement and better overall outcomes than those with longer 2nd ear length of deafness ( > 30 years ) . All participants reported bilateral benefit . CONCLUSIONS Adult cochlear implant recipients demonstrated benefit from 2nd ear implantation for speech recognition , localization , and perceived communication function . Because performance outcomes were related to length of deafness , shorter time between surgeries may be warranted to reduce negative length-of-deafness effects . Future study may clarify the impact of other variables , such as preimplant hearing aid use , particularly for individuals with longer periods of deafness Objective : The purpose of the study was to investigate sound localization with bilateral and unilateral cochlear implants . Design : Sound localization tests were performed on 20 bilaterally implanted MED-EL COMBI 40/40 + users . All subjects were bilaterally implanted during adolescence or later .  Sound localization was tested in the frontal horizontal plane by using 9 equally spaced loudspeakers and speech-shaped noise bursts at r and omized levels . Results : The group of subjects who were bilaterally deafened after 5 to 6 yr of age ( 18 subjects ) showed a statistically significant improvement in sound localization when using both implants , compared with when using only one . The mean deviation between the presentation azimuth and the response azimuth was 16.6 ° when using both implants , which was on average 37.1 ° smaller than when using one implant only . When adjusted for the localization error that was constant across loudspeakers , the mean deviation was 15.9 ° for bilateral implant use , representing an improvement of 30.1 ° over unilateral implant use . Statistical analysis showed that in this group , performance measures were not correlated with subject details such as age at onset of deafness or duration of unilateral implant use . In contrast , subjects who were bilaterally deafened before 6 yr of age ( 2 subjects ) did not show a benefit in sound localization from bilateral implants . Conclusions : Bilateral cochlear implants offer a substantial benefit in sound localization to late-deafened , late-implanted subjects . The very limited data from early-deafened subjects implanted at a later age could suggest that these subjects may not benefit in sound localization from bilateral cochlear implants . It is possible that early implantation for early deafened subjects might allow better acquisition of spatial hearing , thus leading to improved localization performance PURPOSE In this study , the authors sought to compare speech perception and localization in subjects who wear 1 cochlear implant ( unilateral CI ) or 1 cochlear implant and hearing aid ( CI+HA ) and then receive a second cochlear implant ( bilateral CI )  , and to evaluate the importance of the duration between implant surgeries and duration of deafness . METHOD Nine subjects were tested on speech perception  in quiet , and 13 subjects were tested on  speech perception and localization in noise using an array of 8 loudspeakers . All subjects were tested with unilateral CI prior to bilateral implantation and then again with bilateral CI after at least 3 months of bilateral experience . RESULTS No significant difference was found between bilateral CI and unilateral CI on averaged speech perception in quiet performance . A significant benefit was found for bilateral CI on averaged speech perception in noise and on localization . Nonsignificant correlations were found for duration between surgeries , duration of deafness , and duration of bilateral use . CONCLUSIONS Improvements for speech perception and localization played in background noise were indicated for most subjects after they received their 2nd implant . The correlations should be reassessed with a larger number of subjects to appropriately evaluate the effects of duration between surgeries , duration of deafness , and duration of bilateral use 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 significant improvement in speech comprehension scores of 8 % in the bilateral listening condition compared with the scores for the better ear alone . Through assessment of comprehension of coincidental speech in noise and speech in quiet , a significant benefit of binaural redundancy was noted for the group for Oldenburger sentence scores in noise and in quiet compared with unilateral scores for either ear and for the Freiburger monosyllabic words in quiet in comparison with the better ear alone scores . Binaural stimulation also led to a significant improvement in localization ability over either monaural condition , with the root mean square degrees of error reduced by 38 degrees compared with that observed for unilateral stimulation . Conclusion : Similar to what has been observed for bilateral acoustic stimulation in the past , bilateral electrical stimulation provides the foundation for the potential advantages of the head-shadow effect , providing a binaural head-shadow benefit and binaural auditory processing such as binaural redundancy and binaural squelch effects , all of which combine to lead to improved speech comprehension over unilateral listening conditions . The combination of improved speech comprehension and improved localization ability made available through bilateral electrical stimulation provides the necessary foundation to further assist the hearing-impaired listener to better cope with communication in the everyday listening situation both in noise and in quiet Objectives : To investigate whether a squelch effect occurs in the first 3 years after simultaneous bilateral cochlear implantation and to investigate whether this effect increases during follow-up . Study Design : Prospect i ve study as part of a multicenter r and omized controlled trial that compares simultaneous bilateral cochlear implantation to sequential and unilateral cochlear implantation . Setting : Tertiary referral center . Patients : Nineteen postlingually deafened adults . Intervention : Simultaneous bilateral cochlear implantation . Main Outcome Measure : The squelch effect , measured yearly with a speech-intelligibility-in-noise test with spatially separated sources . Bilateral results were compared to unilateral results in which the cochlear implant at the noise side was turned off . The squelch effect was investigated for the patients ’ best performing ear and for the left and right ears separately . Results : In 13 individual patients , a squelch effect was present after 1 year . This number increased during follow-up years . On group level , a squel 
    Output:
    
The literature has shown that duration of deafness , age at onset of deafness , etiology of hearing loss , and preoperative speech perception score are ( inversely ) related to unilateral cochlear implantation outcome in adults .
One would expect that these factors would also affect sequential bilateral implantation outcome .
However , the best available evidence to date shows that advanced age , a long duration of deafness , or a long interval between implantations should not be considered negative factors when considering sequential bilateral cochlear implantation