Stimulus statistical context sensitivity of deviant responses to auditory intensity changes.

Mismatch negativity (MMN) is widely used to study sensory function and its clinically-relevant perturbations, and is modulated by the preceding statistical stimulus context, e.g. standard deviation (SD) of tone frequencies. It is unknown whether similar statistical modulation applies to changes in stimulus intensity; whilst MMN is elicited by intensity changes, intensity is encoded differently to other sensory features, including non-topographic organisation, and absence of single-unit responses to intensity decreases. In two related EEG experiments on normal-hearing volunteers (n = 17/15), we replicate findings from other stimulus properties, showing that MMN to intensity deviants is larger within a low-SD stimulus context. However, we found several differences between high- and low- (vs. standard) intensity deviants. Statistical modulation of high-intensity MMN began earlier, and was robust across both experiments. Low-intensity MMN modulation began later, and was only elicited by one of the two experimental paradigms, which we suspect indicates that adaptation over long timescales and/or higher cortical levels may be required for its statistical modulation.