Mismatch Negativity on Presentation of Amplitude-Modulated Sound Signals

Abstract

The studies reported here addressed analysis of the N1 and P2 components and mismatch negativity (MMN) on discrimination of signals with dynamic changes in intensity in different acoustic contexts. Changes in context in the conditions of the oddball paradigm were created on the basis that each stimulus operated both as a standard and as a deviant in different series, such that the physical differences between signals remained unaltered and their functional relationship flipped to the opposite. Three types of sound signal were used: stimuli with constant intensity and two amplitude-modulated stimuli (linear and stepwise, each with an increase or decrease in intensity). Increases and decreases in the intensity of deviant stimuli induced MMN in the late latency period (>250 msec) without overlap with the N1 component. The difference in signals with linear and stepwise amplitude modulation indexed by mismatch negativity was determined by the direction of deviation in the structure of the sound series. Increment MMN anticipated decrement MMN by 90–100 msec regardless of the type of modulation. Amplitude differences were seen in responses to deviants with stepwise modulation in the context of consistent standards: increment MMN was greater than decrement MMN. The acoustic context affected only increment MMN. These results are consistent with views of the asymmetry in the perception of increasing and decreasing sound intensity, associated with their different biological significance.