Speech and language development following ... - ResearchGate

C. Ouellet, H. Cohen / Journal of Neurolinguistics 12 (1999) 271±288 281Uziel et al. [87] demonstrated that modi®ed open-set recognition was quite evident12 months following the implantation and got even better three years later.Regardless of the percentage of success, open-set discrimination always appearspossible with multichannel implants in most children born deaf or with acquireddeafness, even in hearing-alone conditions [23]. This increased response to soundsin everyday life makes children more alert to interactions with their environment.Three months after wearing the device, children can respond to their names up to63% of the time [53].Although there is generally some improvement in speech perception until 4 or 5years post-implantation, some subjects may, on occasion, show decreased speechperception performance over time, apparently due to a cognitive regressionassociated with age [85]. As was suggested earlier, postoperative performanceappears in¯uenced by the level of preoperative linguistic abilities. In e€ect,patients possessing some preoperative open-set recognition abilities obtainedsigni®cantly higher scores on all recognition measures, at 12 months postimplantation,whereas those with no open-set speech recognition skills before theoperation improved on only half of the measures in the same post-implant period[92]. Speech identi®cation also varies according to word frequency, lexical densityand word length. Lexically easy words (high frequency with few neighbors) arebetter identi®ed than more dicult words (low frequency with many neighbors);word recognition is also better for polysyllabic than monosyllabic stimuli [29].The primary role of cochlear implants is to enable speech perception. Animportant secondary role is to permit speech production and help patients acquireand produce consonant and vowel features which are dicult for individuals withprofound hearing loss (e.g. high vowels, diphthongs, alveolar consonants andfricatives [54]. Language development in implanted prelingually deaf children maybe signi®cantly faster than predictions based only on maturation of unimplantedpeers would suggest. At the 12-month postoperative interval, expressive languagescores have been shown to be higher than the corresponding scores predictedbased on non-operated peers Ð this e€ect was not seen at the 6-month interval.Although implanted children were delayed compared to normal-hearing subjectsat each interval tested, their rate of language growth matched that of hearingcontrols. The gains made by implanted children in expressive language weresimilar to those expected from hearing children and superior to those expectedfrom unimplanted deaf children, at each testing interval from 6 months to 2.5years after implantation. There is, however, signi®cant inter-subject variability inlinguistic abilities following the operation, with some patients reaching nearnormallanguage levels, whereas others remain delayed and show a wide gapbetween linguistic age and chronological age [47].Implant users may exceed their preoperative performance for both intelligibilityand articulation, after experience with a device for from 1 to 4.5 years. Theseimprovements occur for front, middle and back consonants, for stops, fricativesand glides and for voiceless and voiced consonants [16]. The intelligibility ofprelingually deaf children's speech may increase steadily over time, becomingsigni®cantly better than the preoperative performance level after only 6 months.