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Thresholds for detection of frequency modulation coherence and incoherence were measured. The task consisted of detecting a "figure" composed of 1 or more frequency components embedded in a multi-component "ground". The relations among components were either harmonic or inharmonic. Components were modulated in frequency with a random waveform. Freqency modulation width was varied in an adaptive tracking procedure. The components of the figure were always modulated coherently such as to maintain constant frequency ratios. The components of the ground were either modulated coherently or independently of one another. Thresholds for coherent grounds were considered to reflect the sensitivity to modulation incoherence between figure and ground components. Thresholds for incoherent grounds were considered to reflect the sensitivity to modulation coherence among the figure components. The results show that thresholds in the coherent ground conditions depend primarily on the proximity of figure and ground components, suggesting that interactions within auditory channels are used to detect incoherent modulation. Thresholds for incoherent grounds are higher than those for coherent grounds and show that coherently modulated components must fall within the same auditory channels in order for the coherence to be detected, but that information about coherence can be integrated across channels to some extent.