Analysis of correlations between infrasound thresholds and physiological infrasound noise in the ear canal. Each panel shows the analysis for one of the four infrasound frequencies. Each triangle represents the data of one of the 16 listeners. Colors and symbols indicate the absence (blue, downward-pointing triangles) or presence (red, upward-pointing triangles) of ear-generated distortion products at any higher harmonic from f₂ to f₉ of the signal frequency f₁. To quantify physiological infrasound noise, the average spectrum (average of five) was measured in quiet and integrated from 2 Hz to 20 Hz. The integrated power is expressed in dB.