Effect of click stimuli and speech bursts on cortical processing

Late latency responses (LLR) are components of auditory evoked potential (AEP) responses that are found between 50 and 250 milliseconds from the time of stimulation and reflect the responses of the auditory cortex. LLR may be used for threshold estimation as well as to diagnose certain auditory deviations. In view of hardly any studies done on the comparison of LLR with different speech burst stimuli and click stimuli, this study was designed. A total of 12 (24 ears) normal hearing sensitivity subjects were included with no otologic or neurologic symptoms. LLR was recorded with speech burst stimuli/pa/,/ta/,/ka/and click. All the components of LLR were elicited in all the participants with the click stimuli. Among speech burst stimuli,/ta/stimulus was better than/pa/and/ka/stimuli in eliciting all the components of LLR. This difference could be attributed to the spectral energy present in the click stimuli. The difference in latencies when burst stimuli were used can be attributed to spectral differences, duration of stimulus and bandwidth. It can be concluded that the speech burst stimuli can be used to elicit cortical LLR, but responses will be more accurate with click stimuli. The result of this demonstrates the effect of stimulus variation on the LLR response pattern. LLR may be used to objectively measure differences in neural encoding and perception of spectrally different speech sounds.