EEG data were artifact scored for eye movements using a peak-to-peak criterion of 50 mV or greater; artifact associated with gross motor movements over 200 mV peak-to-peak was also scored and eliminated from all subsequent analyses. The data then were analyzed with a discrete Fourier transform (DFT) using a Hanning window of 1s width and 50% overlap. Coherence between frontal sites (Fp1/Fp2, F3/F4, F7/F8) within each hemisphere was computed for the 6–9 Hz frequency band using an algorithm by Saltzberg and colleagues (1986). The 6–9 Hz frequency band is the dominant frequency for infants (Bell & Fox, 1992; Marshall, Bar-Haim, & Fox, 2002), is thought to approximate the alpha band in adults, and has been used by infant EEG researchers to investigate both cognitive and emotional processing (e.g., Bell, 2001, 2002, 2012; Fox, Henderson, Rub, Calkins, & Schmidt, 2001; Orekhova, Stroganova, & Posikera, 2001). Coherence values range from zero to one: High coherence between two EEG signals reflects synchronized neuronal oscillations (suggesting functional integration between neural populations); low coherence reflects independently active populations (suggesting functional segregation). The three intra-frontal coherence values (e.g., Fp1-F3, Fp1-F7, F3-F7) within each hemisphere were averaged to yield a single composite (see Figure 1).
