Speech-evoked cortical auditory responses in children with normal hearing.

OBJECTIVE

Cortical auditory-evoked potentials (CAEPs), an objective measure of human speech encoding in individuals with normal or impaired auditory systems, can be used to assess the outcomes of hearing aids and cochlear implants in infants, or in young children who cannot co-operate for behavioural speech discrimination testing. The current study aimed to determine whether naturally produced speech stimuli /m/, /g/ and /t/ evoke distinct CAEP response patterns that can be reliably recorded and differentiated, based on their spectral information and whether the CAEP could be an electrophysiological measure to differentiate between these speech sounds.

METHOD

CAEPs were recorded from 18 school-aged children with normal hearing, tested in two groups: younger (5 - 7 years) and older children (8 - 12 years). Cortical responses differed in their P1 and N2 latencies and amplitudes in response to /m/, /g/ and /t/ sounds (from low-, mid- and high-frequency regions, respectively). The largest amplitude of the P1 and N2 component was for /g/ and the smallest was for /t/. The P1 latency in both age groups did not show any significant difference between these speech sounds. The N2 latency showed a significant change in the younger group but not in the older group. The N2 latency of the speech sound /g/ was always noted earlier in both groups.

CONCLUSION

This study demonstrates that spectrally different speech sounds are encoded differentially at the cortical level, and evoke distinct CAEP response patterns. CAEP latencies and amplitudes may provide an objective indication that spectrally different speech sounds are encoded differently at the cortical level.