Effect of Speech Stimuli on Aided Late Latency Response in Children with Cochlear Implant

Abstract

The present study aimed to measure the effect of different speech stimuli (/m/, /t/, /g/, & /s/) using auditory late latency response (ALLR) in children with cochlear implants, and compared them with those of typically developing children. The study included 15 unilateral CI recipients and 10 typically developing children (TDC) in the age range of 3-7 years. speech-evoked ALLRs were recorded in CI children and TDC. ALLRs were evoked by all the participants for all speech sounds; the speech-evoked ALLR latencies of P1, N2, and the peak-to-peak amplitude of P1N2 complex were measured and tabulated for analyses. A Mixed model ANOVA was done to check the difference in the performance between CI and TDC groups, and a repeated measure ANOVA was carried out to check differences in ALLR responses in terms of absolute latency and peak to peak amplitude attributed to different speech stimuli, viz. /m/, /t/, /g/, and /s/ for both the CI and TDC groups separately. The results revealed no significant differences in P1 as well as N2 latencies elicited by the speech sounds (/m/, /t/, /g/, and /s/) within the cochlear implant group. However, the peak-to-peak P1-N2 amplitudes evoked by /t/ and /g/ were significantly greater than those elicited by /m/ and /s/, indicating enhanced cortical responsiveness to certain speech sounds in the CI group. In typically developing children, the P1 latency showed no significant differences for any of the speech sounds except /m/ and /t/ sounds. Similarly, N2 latencies did not differ significantly between any speech sounds in the TDC group. Although variability was observed in P1-N2 amplitudes elicited by different speech sounds, none of these differences reached statistical significance. When comparing speech evoked ALLRs between CI children and TDC, P1 latencies were significantly delayed (poorer) for all speech sounds (/m/, /t/, /g/, and /s/) in the CI children in comparison to TDC group. However, no significant differences were found in N2 latencies between the two groups for any of the speech stimuli. The peak-to-peak P1-N2 amplitudes did not show any significant difference between CI children and TDC for any speech stimuli. The absence of significant latency differences across the various speech stimuli in the current study suggests a relatively uniform maturation of cortical auditory processing across the frequency spectrum. This lack of latency difference across different speech sounds may also indicate spectral and temporal processing limitations in CI children. The present study showed the significance of P1 of CAEPs as a biomarker for measuring the development of central auditory pathways among CI recipients. Also, findings of this study suggest that speech sounds with greater energy at stimulus onset (/t/ and /g/) are associated with larger cortical responses. The similar pattern of amplitude variation across speech stimuli seen between both groups suggests that the implanted auditory system retains the capacity to detect and differentiate fine phonetic contrasts, thereby supporting the clinical efficacy of cochlear implantation in promoting functional auditory speech perception.