Frequency-dependent effects of notched-noise forward maskers on pure-tone gap detection

Gap detection thresholds (GDTs) depend on both temporal and spectral stimulus properties, yet the influence of spectrally shaped forward maskers on gap detection across stimulus frequencies has not been systematically characterized. This study examined whether notched-noise (NN) forward maskers alter GDTs in a frequency-dependent manner relative to Quiet and broadband white-noise (WN) masking conditions.

Sixty normal-hearing young adults (18-24 years) completed a 3-Alternative Forced-Choice gap-detection task using tonal markers at 6 frequencies (250-8000 Hz) under Quiet, WN, and NN forward-masking conditions. NN maskers varied in notch center frequency relative to the stimulus frequency. GDTs were estimated from Weibull psychometric-function fits. The primary analysis used a generalized additive mixed model (GAMM) to characterize the nonlinear effect of signed notch offset on GDT change relative to Quiet.

WN was descriptively associated with higher GDTs than Quiet across all frequencies. NN conditions were often associated with lower GDTs than Quiet, and this effect varied nonlinearly across stimulus frequencies and notch positions (edf = 21.07, F = 120.57, p < 0.001; adjusted R² = 0.757). The resulting frequency-specific gap-detection profiles ranged from localized non-monotonic patterns at lower frequencies to broader profiles at higher frequencies.

Spectral shaping of a forward masker systematically altered gap-detection performance in a frequency-dependent manner. The finding that some NN conditions yielded GDTs below Quiet is consistent with spectrally broad context effects and may reflect precursor-related adaptation processes not fully captured by a simple within-channel account.