Mismatch negativity to inclusions and omissions of stimulus features

Two experiments were run to determine the effects of addition or removal of a stimulus feature on mismatch negativity (MMN). In the first experiment, a deviant stimulus was constructed by adding a click to a white noise standard stimulus. In the second experiment, the deviant was constructed by subtracting the click from the standard. In different conditions, the intensity of the click was varied. When the deviant was constructed by the addition of a click, a significant MMN was evident in those conditions in which click-to-noise ratio exceeded 1.0. When the deviant was constructed by the subtraction of the click, a significant negativity was found only when the click-to-noise ratio was very large. However, this negativity was accompanied by only a small polarity inversion at the mastoid. The MMN is thus best elicited when the deviant stimulus contains a new afferent element not present in the standard stimulus.