Background:
A reduced amplitude mismatch negativity (MMN) component of the auditory event-related potential (ERP) is repeatedly observed in individuals with schizophrenia. MMN amplitude also declines significantly with age in healthy adults. Our group is endeavoring to understand whether the factors underlying MMN reduction are common or unique. In this study, we explored the effect of deviant probability on group differences.
Methods:
ERPs were recorded from 43 individuals diagnosed with schizophrenia and 42 age-matched controls. Sound sequences containing duration, intensity and frequency deviant sounds at low (6%) or high (20%) probability were presented while participants viewed a movie with low-level soundtrack.
Results:
A repeated-measures ANOVA was used to compare MMN amplitude across groups (patients/ controls) and deviant type (duration/frequency/intensity) and probability (low/high) with age as a covariate. There were significant main effects of probability and deviant type both modified by age and a main effect of group modified by probability. Patients produced significantly smaller MMN responses to low- but not high-probability deviants. Age was a significant covariate in the low-probability but not the high-probability condition with the differences being more pronounced for frequency and intensity MMN than duration MMN.
Conclusions:
MMN amplitude was significantly reduced in schizophrenia vs. controls for the low-probability condition only (ie when under conditions of increased repetition of the standard sound). The age-related decline in MMN was also most pronounced under these conditions. The results are discussed with respect to current research into memory-based and discrimination-based conceptualizations of the MMN.
