An interferer nearest the masker in frequency most strongly elevates signal thresholds.

Evidence

Threshold was highest when the spectral distance masker-target and interferer-masker threshold was the same. It was 4.5 dB lower when the interferer was positioned 30 Hz instead of 100 Hz below the masker. A similar trend was observed for the dichotic 800-Hz target (bottom right panel) although the difference between the highest threshold for an interferer at 100 Hz below the masker and the lowest threshold without interferer was only 8 dB whereas it was 11.5 dB for the diotic 800-Hz target. — Dijk, Pim van, Physiology, Psychoacoustics and…, 3484