Effects of sequential and temporal probability of deviant occurrence on mismatch negativity

The mismatch negativity (MMN) increases in amplitude as the probability of deviant occurrence decreases. It is unclear whether the determining variabl e is sequential probability (i.e. the probability of a deviant within a num ber of standards) or temporal probability (i.e. the probability of a devian t within a period of time). Eight subjects heard a train of frequently occu rring 1000 Hz standard tones. The probability of a 1100 Hz pitch deviant wa s manipulated. In one condition the stimulus-onset-asynchrony (SOA) was 150 ms, with temporal probability of deviant occurrence being either 1/9.00, 1 /4.50, 1/2.25, or 1/1.25 s (sequential probability being 1/60, 1/30, 1/15, or 1(deviant)/7.5(standards), respectively). In another condition the SOA w as 600 ms, with temporal probability being either 1/9.00, 1/4.50, or 1/2.25 s (sequential probability being 1/15, 1/7.5, or 1/3.75, respectively). In a final condition, the SOA was 2400 ms with temporal probability being 1/9. 00 s (sequential probability 1/3.75). Both sequential and temporal probabil ities had a marked effect on the MMN. When a deviant occurred every 2.25, 4 .50, or 9.00 s, the MMN increased as temporal probability decreased. When a deviant occurred once every 7.5 or 15 standards, the MMN was larger for lo wer sequential probability, but the effect was not significant. Nevertheles s, when temporal probability was held constant at 1/9.00 s, the MMN increas ed as sequential probability decreased. At rapid rates of stimulus presenta tion, the MMN was largest. However, it was attenuated when the probability of deviant occurrence was very high perhaps due to the refractoriness of it s generator. At the slowest rate, the MMN was diminished perhaps due to mem ory decay for the standard stimuli. (C) 2001 Elsevier Science B.V. All righ ts reserved.