Validity of correction factors applied to auditory steady-state responses (ASSRs) in normal hearing adults in chartr EP system.

OBJECTIVES: Even though many patients undergoing auditory steady-state response (ASSR) testing have some degree of hearing loss, some have normal hearing and ASSR often overestimates the behavioral thresholds in this group. In most commercial ASSR systems such as Chartr EP, a default correction factor is applied to compensate for this difference. Little is known, however, as how the correction factor compensates for the difference between ASSR and pure tone audiometry (PTA) thresholds as a function of carrier or modulation frequency (MF) in a commercial ASSR system. Our goal is to evaluate this relationship.
METHODS: Twenty-four normal hearing adults were examined for both PTA and ASSR (Chartr EP system, GN Otometrics). ASSR thresholds were obtained at three MFs (20, 40, and 80 Hz). The difference scores were obtained by subtracting PTA from ASSR thresholds at each frequency for each subject. The corrected ASSR thresholds, then, were compared with the PTA thresholds across MFs and carrier frequencies.
RESULTS: The default correction factors in the ASSR equipment differed significantly from the difference scores at all MFs and carrier frequencies (n = 24, p < 0.005). The correlation between corrected ASSR and PTA thresholds at most MFs and carrier frequencies were medium to poor.
CONCLUSIONS: At most MFs and carrier frequencies, the default correction factors defined by the manufacturer do not compensate for the difference between ASSR and PTA thresholds in normal hearing adults. The use of the default correction factors in Chartr EP system for the normal hearing adults needs special considerations.