Measuring duration mismatch negativity.

OBJECTIVE

Automatic comparisons of sound duration in auditory sensory memory are typically investigated by comparing event-related potentials (ERPs) to standard and deviant stimuli presented in oddball blocks. Deviants elicit mismatch negativity (MMN). This procedure might overestimate an MMN contribution reflecting automatic sensory memory processes because of differential states of refractoriness of respectively recruited neural populations [Neuroreport 1996;7:3005; Psychophysiology 2001;38:723]. Here, memory-comparison-based Duration MMN contributions were investigated using various experimental protocols.

METHODS

Memory-comparison-based first-order Duration MMN was investigated using 4 blocked conditions: (a) descending Deviant (100 ms, P=0.14), 150 ms Standard; (b) reverse ascending Deviant (150 ms), 100 ms Standard; (c) Control comprised of 7 equiprobable durations between 25 and 175 ms; and additionally (d) equiprobable tones between 100 and 400 ms. Using the former 3 conditions, Deviants, Standards and Controls were physically identical.

RESULTS

Comparing Deviants and Controls excluded potential refractoriness effects, and a decomposition of memory-comparison-based MMN and residual MMN was demonstrated. Genuine Duration MMN was also obtained in the deviant-standard-reverse comparison.

CONCLUSIONS

Using a blocked control condition yielded equivalent results to reversing the role of deviant and standard in two separate oddball blocks. Using the reverse ascending deviant condition is thus sufficient as a control.