Auditory Cortical Temporal Processing Abilities in Young Adults

Purpose: To evaluate whether cortical encoding of temporal processing ability, using the N1 peak of the cortical auditory evoked potential, could be measured in normally hearing young adults using three paradigms: voice-onsettime, speech-in-noise and amplitude-modulated broadband noise. Research design: Cortical auditory evoked potentials (CAEPs) were elicited using: (1) naturally produced stop consonant-vowel (CV) syllables /da/-/ta/ and /ba/-/pa/; (2) speech-in-noise stimuli using the speech sound /da/ with varying signal-to-noise ratios (SNRs); and (3) 16 Hz amplitude-modulated (AM) BBN presented in two conditions: (i) alone (representing a temporally modulated stimulus) and (ii) following an unmodulated BBN (representing a temporal change in the stimulus) using four modulation depths; (4) Behavioural tests of temporal modulation transfer function (TMTF) and speech perception using CNC word list were carried out. All stimuli were presented at 65 Db SPL in the sound field. Study sample: Participants were adults (12 Females and 8 Males) aged 1830 years with normal hearing. Results: Results showed: (1) a significant means difference in N1 latency (p<0.05) between /da/ vs. /ta/ and /ba/ vs. /pa/; (2) significant N1 latency prolongation with decreasing signal-to-noise ratios for the speech sound /da/; and (3) the N1 latency did not significantly change for different modulations depths when measured for the AMBBN alone or when following a BBN. Conclusion: Changes in the N1 latency provide a measure of temporal changes in a stimulus for VOT and speech-in-noise. N1 latency could be used as an objective measure of temporal processing ability in individuals with temporal processing disorder who are difficult to assess by behavioural response.