Mean (symbols) and standard deviation (error bars) of the modulation depth at threshold for an 8 Hz modulated 64 Hz carrier (circles, top panel) and the change in threshold (masking) when measured in the presence of an 8 Hz sinusoid presented at an SL of 9 dB (triangles, bottom panel). Right-pointing and left-pointing triangles indicate the masking when infrasound and modulation are presented in phase and in antiphase, respectively. As in Figure 1, open symbols indicate single-subject data, filled symbols on the far right average data of all listeners. Error bars indicate the mean ± one standard deviation. Colored boxes in the bottom panel quantify the strength of the phase effect. Red boxes indicate a stronger masking for 0° and green boxes for 180°. The listeners were sorted and numbered based on this phase effect.