Figure 3.

Averaged difference waves (deviant − standard) from infants. Waveforms from left and right frontal (FL, FR), central (CL, CR), parietal (PL, PR), and occipital (OL, OR) scalp regions are shown filtered between 1.5 and 20 Hz. The y-axis marks the onset of the first tone and the gray line the onset of the second tone in each pair. The dipolar pattern of MMN, with anterior negativity and posterior positivity, can be seen peaking at 166 ms after the onset of the second tone in 7-month-old infants and at 192 ms in 4-month-old infants, but not in 3-month-old infants. The shaded area over the waveforms marks the time periods during which the difference wave at the right frontal (FR) region is significantly different from zero (338 ms to 393 ms for 7-month-old infants and 365 ms to 423 ms for 4-month-old infants). In 7-month-old infants, seven of the eight regions showed significant MMN; in 4-month-old infants, six of the eight regions showed significant MMN; in 3-month-old infants, none of the regions showed significant MMN. In the 4- and 7-month-old infants, there appears to be a frontally positive component following the MMN. This component has been observed in other studies of MMN (Trainor et al., 2001) and may correspond to the adult P3a component, reflecting capture of attention. Note that we doubled the number of infants in the 3-month group to obtain greater power to examine small effects, but no suggestion of an MMN response emerged. The results indicate that cortical responses to pitch of the missing fundamental emerge between 3 and 4 months of age.