Distortion-product otoacoustic emission (DPOAE) suppression tuning curves (STCs) were measured in 65 hearing-impaired (HI) subjects at f 2 frequencies of 2.0, 2.8, 4.0, and 5.6 kHz and L 2 levels relative to sensation level (SL) from 10 dB to as much as 50 dB. Best frequency, cochlearamplifier gain (tip-to-tail difference, T-T), and tuning (Q ERB ) were estimated from STCs. As with normal-hearing (NH) subjects, T-T differences and Q ERB decreased as L 2 increased. T-T differences and Q ERB were reduced in HI ears (compared to normal) for conditions in which L 2 was fixed relative to behavioral threshold (dB SL). When STCs were compared with L 2 at constant sound pressure levels (dB SPL), differences between NH and HI subjects were reduced. The large effect of level and small effect of hearing loss were both confirmed by statistical analyses. Therefore, the magnitude of the differences in DPOAE STCs between NH and HI subjects is mainly dependent on the manner in which level (L 2 ) is specified. Although this conclusion may appear to be at odds with previous, invasive measures of cochlear-response gain and tuning, the apparent inconsistency may be resolved when the manner of specifying stimulus level is taken into account.

Growth of distortion-product otoacoustic emission suppression was measured in 65 subjects with mild-to-moderate sensorineural hearing loss (HI). Measurements were made at four probe frequencies (f 2 ) and up to five L 2 levels. Eleven suppressor frequencies (f 3 ) were used for each f 2 , L 2 combination. These data were compared to data from normal-hearing (NH) subjects (Gorga et al., 2011a). In both NH and HI subjects, growth of suppression depended on the relation between f 2 and f 3 , such that the slope was close to one when f 3 % f 2 , steeper than one when f 3 < f 2 , and shallower than one when f 3 > f 2 . Differences in growth of suppression between NH and HI subjects were not observed for fixed f 2 , L 2 combinations, however large differences were observed in suppressor "threshold" when compared at the same probe sensation level (dB SL). Smaller group differences were observed when compared at the same probe sound-pressure level (dB SPL). Therefore, the extent of these differences depended on how probe level (L 2 ) was specified. When the results from NH and HI subjects are compared with each other and with psychophysical studies of masking, differences are observed that have implications for the remediation of mild-to-moderate hearing loss.

Norms for the DOSO are recommended for evaluating hearing aids with more recent technologies.