The analysis at anterior sites revealed significant effects of group and task x group, which originated from reduced N2 sink amplitude for patients, particularly for the tonal task (M ±SD, controls vs. patients, −0.96 ±1.37 vs. −0.27 ±1.27) but not for syllables (−0.01 ±1.06 vs. 0.04 ±1.01). Apart from a highly significant task main effect that simply confirmed the presence of N2 sink for tones but not syllables at these sites, there was also a highly significant response mode x hemisphere interaction (Figure 4). Simple hemisphere main effects for each response mode revealed right-greater-than-left N2 sinks for left press (LH vs. RH, −0.18 ±1.14 vs. −0.54 ±1.46; F[1,44] = 10.6, p = .002) and silent count (−0.14 ±0.95 vs. −0.30 ±1.25; F[1,44] = 3.73, p = .06), but left-greater-than-right N2 sinks for right press (−0.41 ±1.25 vs. −0.23 ±1.36; F[1,44] = 3.89, p = .05). Although there was no significant overall task x hemisphere interaction at these anterior sites, a simple interaction effect at FC5/6 (F[1,44] = 6.34, p = .02) stemmed from a right-greater-than-left N2 sink for tones (LH vs. RH, −0.44 ±1.33 vs. −0.48 ±1.34), and vice versa for syllables (−0.01 ±0.95 vs. 0.31 ±1.15).
