Application of cross-correlation function in the evaluation of objective MLR thresholds in the low and middle frequencies

In this study, the cross-correlation function was applied in the evaluation of MLR thresholds in the low and middle frequencies. The parameters of the cross-correlation function consist of the correlation coefficient at a lag-time of zero (RO), the maximum correlation coefficient (RM), and the latency delay on the lag-time axis at the point of the maximum correlation coefficient (DL). The normal limits of the parameters of cross-correlation at the MLR threshold level, which was identified by visual detection across frequencies, were obtained in normal-hearing and hearing-impaired subjects. The cross-correlation functions for two traces were also performed below threshold level. All cross-correlation parameters (RO, RM and DL) below threshold level were outside normal limits in 91% of all the subjects. The incidence of the only RM or DL parameter value within normal limits was 6% or 3% of all cases at the subthreshold level. Correlation data allow precise measurements of the MLR threshold and enhance the sensitivity of the definition of the MLR threshold. In addition, our study provides quantifiable information for estimating MLR threshold.