Auditory M50 and M100 responses to broadband noise: functional implications.

The functional significance of the M50 and M100 auditory evoked fields remains unclear. Here we report auditory evoked field data from three different studies employing wide-band noise stimuli. We find that, for the same stimuli, the strength of the M100, as well as its lateralization, are task-modulated. The M50, in contrast, shows three properties: It is dramatically more pronounced for noise stimuli than for pure tones, does not seem to be task dependent, and, is significantly stronger in the left hemisphere in all task conditions. These contrasting patterns of activation shed light on the properties of the response-generating mechanisms and suggest roles in the process of auditory figure-ground segregation.