Objective: To investigate whether children implanted in the first year of life show higher levels of speech perception than later-implanted children, when compared at the same ages and to investigate the time course of sensitive periods for developing speech perception skills. More specifically, to determine whether faster gains in speech perception are made by children implanted before 1 year old relative to those implanted at 2 or 3 years.
Study design: Retrospective cohort study.
Setting: Tertiary academic referral center.
Patients: 117 children with congenital profound bilateral sensorineural hearing loss, with no additional identified disabilities.
Intervention: Cochlear implantation in the first, second, or third year of life.
Main outcome measure: Development curves showing Lexical Neighborhood Test (LNT) word identification scores as a function of age.
Results: Children implanted within the first year of life have a mean advantage of 8.2% LNT-easy word scores over those implanted in the second year (p < 0.001) and a 16.8% advantage in LNT-easy word scores over those implanted in the third year of life (p < 0.001). These advantages remained statistically significant after accounting for sex, residual hearing, and bilateral cochlear implant use. When speech perception scores were expressed as a function of "hearing age" rather than chronological age, however, there were no significant differences among the 3 groups.
Conclusion: There is a clear speech perception advantage for earlier-implanted children over later-implanted children when compared at the same age but not when compared at the same time after implantation. Thus, the sensitive period for developing word identification seems to extend at least until age 3 years.