Demographics and clinical characteristics

As proposed by our hypothesis, CI before and after the age of two years were classified as “early intervention” and “late intervention,” respectively. Additionally, an individual’s experience with device use was defined as the time interval between turning on the CI and postoperative P1 testing. Typically, ANSD patients with various underlying etiologies who receive early implantation before the age of two years have also been shown to have normalized age-appropriate P1 waves at approximately six months postoperatively [17]. Considering this, we randomly hypothesized that one year would be sufficient to induce normal P1 waves, as this duration is twice as long as six months. Given this, our cohort was further classified into those with “sufficient experience” (i.e. > 1 year) and “insufficient experience” (i.e. < 1 year) to identify the stark difference in P1 maturation, depending on an individual’s experience with device use. In our cohort, three subjects showed a remarkably short experience with their device (approximately six to seven months), while the remaining subjects had relatively long experience with their device (more than two years). Based on our criteria, subjects were divided into three groups: early intervention with sufficient experience (group 1, N = 3), early intervention with insufficient experience (group 2, N = 3), and late intervention with sufficient experience (group 3, N = 4) (Table 1). The median age at CI was 12 months for both groups 1 and 2 (range, 10–14 months) and 36 months for group 3 (range, 25–400 months). The average follow-up duration between CI and CAEP testing for groups 1, 2, and 3 was 36 months (range, 36–52 months), 7 months (range, 6–10 months), and 82 months (range, 26–100 months), respectively. All subjects in groups 1 and 2, as well as two of the four subjects in group 3, underwent bilateral simultaneous CI, whereas the remaining two subjects in group 3 underwent bilateral sequential CI. Moreover, there was no difference in the preoperative hearing status (unaided and aided) between the two adult subjects (Subjects 9 and 10) for which behavioral audiometry was possible.

Abbreviation: ANSD, auditory neuropathy spectrum disorder; CI, cochlear implantation; S/E, speech evaluation; CAEP, cortical auditory evoked potential; CAP, categorization of auditory performance; IT-MAIS, Infant-Toddler Meaningful Auditory Integration Scale; SIR, speech intelligibility ratio; Y, year; mo, month; M, male; F, female; NA, not available.

* Note that the two subjects (subject No. 5 and 6) in group 2 were available to evaluate the additional P1 measurement at 5 months after their initial evaluation. Their follow-up CAEP testing was performed at 11 and 12 months, respectively, after cochlear implantation.