To develop indices that identify factors that control gain and influence the limits of dynamic range. In a series of studies, participants were presented with sequences containing two sounds that alternate roles as a rare deviant (p=0.125) and common standard (p=0.875). In slow sequences roles alternated every 480 tones (2.4 minutes) and in fast sequences, every 160 tones (0.8 minutes). Theoretically MMN should be larger in slow than fast changing sequences due to longer-term stability in the standard enabling higher growth in predictive confidence.
In several studies we have observed an order-dependent bias in how sequence type affects MMN size. MMN in slow sequences is indeed larger than in fast sequences but only for the sound that is the first encountered deviant. We have also been able to demonstrate that this bias is influenced by priming behavioural relevance for the sounds. This order-dependent bias represents a previously unknown influence on MMN size and is susceptible to manipulations of stimulus salience. Uncovering how the bias limits gain can provide a window into why growth in MMN size is limited in schizophrenia.
