Figure 2.

Averaged ERP responses from adults. Top, The averaged response from the right frontal region to standard tone pairs (with rising pitch) and to deviant tone pairs (with falling pitch if the missing fundamental is perceived), filtered between 1.5 and 20 Hz. Because the auditory cortex is located around the Sylvian fissure, the orientation of axons in this region gives rise to electrical fields at the surface of the head that have a frontal positive or negative pole concurrent with a posterior polarity reversal. The y-axis marks the onset of the first tone and the gray line the onset of the second tone in each pair. Both standard and deviant waveforms show similar P1, N1, and P2 responses to both tones. Deviant waveforms show an additional MMN in response to the deviants, indicating clear processing of the pitch of the missing fundamental in adults. Middle, The averaged difference waveform (deviant − standard) at the right frontal region. The shading marks the time periods during which the waveform is significantly different from zero. It can be seen that at the right frontal site, the standard and deviant waves differ only between 108 and 167 ms, at the time of the MMN. Bottom, The waveforms from left and right frontal (FL, FR), central (CL, CR), parietal (PL, PR), and occipital (OL, OR) scalp regions. The MMN response reverses polarity at the back of the head, consistent with primary generators along the Sylvian fissure in left and right auditory cortices.