INDIVIDUAL-DIFFERENCES AND THE RELIABILITY OF 2F1-F2 DISTORTION-PRODUCT OTOACOUSTIC EMISSIONS - EFFECTS OF TIME-OF-DAY, STIMULUS VARIABLES,AND GENDER

Distortion product otoacoustic emissions (DPOAEs) measured from the ea r canal can be a sensitive tool to detect changes in cochlear function over time. However, if multiple-measurement procedures are to be usef ul clinically, testing needs to be reliable and sources of variability within individuals should be known. Herein, the influence oi time-of- day (TOD), stimulus frequency, stimulus sound pressure level (SPL), an d gender were evaluated on 2f1-f2 DPOAE amplitude in 16 adult voluntee rs with normal hearing, The effects of oral temperature and resting-pu lse rate were also assessed. This study demonstrated a TOD main effect , with a period approximating one cycle-per-day. The magnitude of this effect averaged less than one dB and was not dependent on stimulus (f requency or SPL) or participant variables (gender, oral temperature, o r resting-pulse rate), nor was it synchronized to a particular point-i n-time, Stimulus level and gender effects on DPOAEs across frequency w ere also observed, Using generalizability theory (GT), DP iso-level/fr equency profiles (DPILFPs) were found to be reliable measures within-s ubjects over a contiguous 24-hour time period. Significant and reliabl e between-subject differences were also documented. This study demonst rates the influence of stimulus and participant variables, quantifies the within-subject reliability over a 24-hour lime period, and confirm s that significant and reliable between-subject differences exist on D POAEs across frequency; SPL, and gender.