New developments in speech processing: Effects on speech perception abilities in children with cochlear implants and digital hearing aids

The aim of this study was to determine the unaided puretone average (PTA) above which a child will exhibit significantly better speech recognition with a cochlear implant than a digital hearing aid. Children with PTA's (.5, 1.0, 2.0 kHz) in the severe to profound range, wearing Digital Signal Processing (DSP) hearing aids with Wide Dynamic Range Compression (WDRC) or a Nucleus 24 or Clarion cochlear implant system, were evaluated using a speech perception test battery administered at intensity levels representative of raised and soft speech levels. Fifty-two children (age 5–15 years) participated: 26 with unaided PTA's from 60 to 98 dB HL using DSP hearing aids and 26 with pre-implant unaided PTA's from 93 to 120 dB HL using cochlear implants. Several outcome measures were obtained twice to assess test-retest reliability. The Lexical Neighborhood Test (LNT) was analyzed as the major outcome variable due to high test-retest reliability. Multiple regression with repeated measures analyses of LNT scores revealed a significant Level effect, as well as Device x Level and Device x Time interactions. The Level effect is explained by reduced audibility at 50 dB SPL. With unaided PTA as a covariate, intersection between the regression lines for the two devices was dependent upon Level and Time. The unaided PTA at which the lines intersected was 82 and 90 dB HL for a 70 dB SPL level and 85 and 68 dB HL for 50 dB SPL at time 1 and 2, respectively. For the DSP Hearing Aid Group, lower LNT scores at 50 dB SPL and Time 2 may be explained by reduced audibility caused by feedback and insufficient gain. Assuming that LNT scores at 50 dB SPL at Time 2 are representative of long-term hearing of soft incidental speech that is essential for language learning and fluent communication, the children using DSP hearing aids in this study with PTA's of 88 dB HL would be expected to have significantly higher LNT scores with a cochlear implant. These results should be further examined with research efforts focusing on early intervention with optimally fitted DSP hearing aids and cochlear implants.