Methodological Determinants of Objective-Subjective Discrepancies in HPD Attenuation

Evaluating hearing protection device (HPD) attenuation requires integrating physical measures, such as objective microphone-in-real-ear (MIRE), with subjective psychophysical estimates, such as real-ear attenuation at threshold (REAT). Objective-subjective discrepancies are commonly interpreted as reflecting the contribution of bone-conduction pathways, which may limit the total achievable attenuation under high-occlusion conditions. However, findings across studies are inconsistent, and recent data from a 30-participant study further challenged a simple one-directional interpretation. Frequency-dependent crossovers were observed: MIRE indicated greater attenuation than REAT at some frequencies, whereas the opposite pattern emerged at others.

This preliminary work examines whether such discrepancies reflect a fixed measurement bias or arise from methodological and physical factors. Normal-hearing participants were tested under controlled sound-field conditions. Objective real-ear measurements were used to assess the effects of input level, stimulus type, and HPD type on measured attenuation. In parallel, a suprathreshold loudness-matching, or loudness-balance, paradigm was used to examine whether estimating subjective attenuation at levels more comparable to objective measurements alters the attenuation pattern relative to standard threshold-based assessment. Although loudness balance has been used in early ear-protector research, it is rarely integrated into contemporary MIRE/REAT comparisons.

Initial findings suggest that HPD attenuation discrepancies are context-dependent. Objective profiles varied with HPD type and stimulus characteristics, while behavioral estimates differed between REAT and loudness matching. These results support a broader methodological framework in which objective measurements, threshold-based estimates, and suprathreshold loudness judgments are interpreted as complementary, rather than interchangeable, measures of protected listening.