The effect of 1/f fluctuation in inter-stimulus intervals on auditory evoked mismatch field

We studied the effect of the exponent of the fluctuation in the inter-stimulus interval (ISI) on the elicitation of auditory evoked mismatch fields (MMF) with two sounds with alternating frequency. ISI times were given by three types of fluctuation, 1/f0, 1/f1, 1/f2, and with a fixed interval (1/f∞). The root mean square (RMS) value of the MMF increased significantly (F(3/9) = 4.95, p = 0.027) with increases in the exponent of the fluctuation. Increments in the regularity of the fluctuation provoked enhancement of the MMF, which reflected the production of a memory trace, based on the anticipation of the stimulus timing. The gradient of the curve, indicating the ratio of increments between the MMF and the exponent of fluctuation, can express a subject's capability to extract regularity from fluctuating stimuli.