that direct differentiation on an interpolated function is unnecessary; and (4) robust to noise. Compared to the second order spline estimation (Babiloni et al., 1995), the local polynomial approximations is better for cleaner data with high signal-to-noise-ratio (SNR), such as averaged ERPs, but this method fares poorly for very noisy data with poor SNR, such as single trials (cf. Wang and Begleiter, 1999).
