Evaluating the audible contrast threshold for predicting speech-in-noise with earplugs in young adults: a pilot study

The Audible Contrast Threshold (ACT) is a language-independent measure of sensitivity to spectro-temporal modulation and has been proposed as an alternative predictor of speech-in-noise performance. Strong relationships between modulation detection and sentence-in-noise scores have been reported in older adults with sensorineural hearing loss, but it is unknown whether similar relationships exist in young normal-hearing adults or under conditions that simulate conductive attenuation. Eight young normal-hearing female participants (mean age 25.1 years) completed ACT, pure-tone thresholds, and an adaptive monosyllabic Hebrew speech-in-noise test in two listening conditions: unoccluded and occluded with foam earplugs. Noise was presented at 85 dB SPL in both conditions. Hearing protection elevated thresholds as expected and significantly degraded SNR50 performance. ACT values, however, remained unchanged across conditions. Correlation analyses (Pearson and Kendall's tau) revealed no association between ACT and SNR50 in either listening mode. These findings suggest that ACT captures a suprathreshold temporal-contrast sensitivity mechanism that remains robust under attenuation but does not predict speech-in-noise performance in young normal-hearing listeners. Implications for operational use, fit-testing applications, and the distinction between conductive and sensorineural mechanisms are discussed.