Abstract Event-related potentials were recorded to tones that subjects ignored while reading a book of their choosing. In all conditions, 90% of the tones were 100 msec in duration and 10% of the tones were 170 msec in duration. In a control condition, a customary oddball paradigm was used in which all of the tones were identical except for the longer duration tones. In two conditions, the tones varied over a wide range of tonal frequencies from 700 to 2050 Hz in 10 steps of 150 Hz. In another condition, the tones varied over the same frequencies but also varied in intensity from about 60 to 87 dB in steps of 3 dB. Thus, there was no "standard" tone in the sense of a frequently presented tone that had identical stimulus features. A mismatch negativity (MMN) was elicited in all conditions. The data are discussed in terms of the storage of information in the memory upon which the MMN is based.