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278C. Ouellet, H. Cohen / Journal of Neurolinguistics 12 (1999) 271±288intervention may be required to meet these conditions. The cochlea is alsoexamined to detect any malformation or intracochlear ossi®cation. Finally,exclusionary factors may be identi®ed in the psychological assessment, such asundetected psychosis, organic brain dysfunction or mental retardation.5. Mediating factorsSeveral factors appear to in¯uence the bene®ts of a cochlear implantation andhelp explain, alone or in combination, the large between-subject di€erences inimplant outcome and the variance in patients' linguistic improvement. Amadori etal. [1] de®ned a number of predictors concerning a broad range of linguisticperformances: (1) age at onset of deafness, with postlingual patients being moreecient than prelingual ones; (2) duration of deafness, with better results beingassociated with a shorter period of deafness; and (3) length of electrode insertionand activation, with poorer performance usually being associated with fewer than10 active electrodes. For other researchers, the most important predictive factorsare auditory nerve survival [44] and responsiveness of the central nervous system[86].A moderate correlation between speech recognition performance in adults andelectrical thresholds, dynamic ranges and the number of active electrodes has beennoted [20,28], whereas patients' willingness and motivation were also found to bestrongly associated with speech understanding [20,30]. Visual informationprocessing skills, knowledge of nonverbal communication strategies and activemanagement of one's healthcare are further factors, alone or in combination, thatcould account for the variability in postoperative scores [21]. Finally, there isapparently no relationship between IQ alone and implant outcome.It might be expected that post-implant linguistic abilities would depend uponthe age at which someone went deaf. However, Osberger et al. [55] did not ®nddi€erences in speech perception performance between children born deaf(congenitally deafened) and those deafened before the age of 3 (prelinguallydeafened children). They only ®nd signi®cantly better skills on tests of stresspattern, closed- and open-set discrimination in children deafened after the age of5. In contrast to these results, Nikolopoulos et al. [50] found lower scores inprelingually deaf children compared to congenitally deaf children on a scaleassessing the developing use of post-implant audition. Ito et al. [27] demonstrateda delayed speech comprehension performance in prelingually deaf patientscompared with postlingually deaf ones; nevertheless, the former group alsoprogress in the ®rst years after implantation, at a slower but still continuous rate[33].The age at which patients are implanted is also a critical variable. Prelinguallydeafened candidates implanted in adolescence or adulthood do not score abovechance levels on word and sentence identi®cation tests without lip-reading. Thismay be due to their lifestyle and manual communication experience, to social andcultural in¯uences and/or to the e€ects of longer auditory deprivation since birth
C. Ouellet, H. Cohen / Journal of Neurolinguistics 12 (1999) 271±288 279[8,14]. There may also be a trend towards non-use of the device in patientsimplanted during adolescence [46]. However, Summer®eld and Marshall [76] failedto replicate this association between age at implantation and performance.Duration of deafness has been found to have the most robust association withperipheral (the number of ganglion cells) and central determinants (responsivenessof the nervous system, potential for relearning and memory for sounds of speech)of good performance with the device [86]. Subjects with a shorter duration ofauditory deprivation tended to perform better on tests of speech perception thanthose with longer periods of deafness [72,73]. However, this factor has been foundto account for only about 20% of the speech understanding variance [86].Finally, experience with implant usage will also determine the course ofimprovement of response to the device over time. Implant performance is usuallymeasured between one week and one month after device activation Ð this is thetime required to program the processor optimally [86]. Speech perception maysigni®cantly improve after 6, 12 and 24 months of implant use [89]. Recognitionperformance generally increases over the ®rst 9 months of implant experience andabout half of this improvement occurs within one month of implantation. Thetime frame for improvements in performance with second-generation implantsystems may extend over 2 or 3 years, with large individual di€erences observed inthe pattern of performance evolution [86]. For instance, data suggest thatimprovements in closed-set recognition do not occur before 1 year of implant usein prelingually deafened children; open-set speech recognition takes even longer[18,45,88] because of the complex linguistic and auditory processes involved.However, Staller et al. [74] found signi®cant improvements in speech perceptionskills after only 6 months of device experience. As for speech production, it mayincrease throughout the ®rst 4 months but progress slows down at 1 year.However, the possible rapid improvements from day 1 to days 30 and 120 in aprelingually deaf group suggest that cochlear implants allow immediate bene®ts inspeech production [79] Ð but these discrete changes do not increase the listener'scapacity to understand an implanted child's speech until after about 2.5 yr ormore of device use [64].6. Linguistic consequences of cochlear implantationCochlear implants enable di€erent degrees of improvement for deaf patients inthe areas of speech and language perception, production and comprehension,depending upon the extent of their hearing loss and other variables. These areasinclude several subskills, which develop in a relatively hierarchical order. Althoughthe immediate response following activation of the device is not always clear,subsequent progress in auditory discrimination is soon evident, with voweldiscrimination reaching 100% in 8 months in certain circumstances. Articulationand intonation also improve, as well as reception of sounds from the environment[51]. Gains in receptive and expressive language may exceed those predicted frommaturation alone in children after 12 months of device use, with a language
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