Automatic detection of frequency change is invariant over a large intensity range.

The influence of stimulus intensity on the automatic detection of frequency change was studied. Ten human subjects were presented with a high-probability standard tone (700 Hz) and a low-probability deviant tone (750 Hz). In a between-block design, the intensity of the auditory stimuli was varied over a 40 dB range. The frequency deviant elicited the mismatch negativity (MMN), an event-related brain potential component indicative of automatic change detection in the auditory cortex. The MMN for a frequency change was even elicited in low-intensity blocks and it did not significantly vary with intensity. These results suggest that the frequency MMN is sensitive to the informational content of a change not to the total amount of stimulus energy. Furthermore, the data imply that an efficient encoding of frequency information, which underlies the change detection mechanism, takes place even with weak sensory stimulation.