200-400 msec

Later significant effects of the Intentional-age and Intentional-gender discrimination tasks were found between about 200 and 400 msec latency at occipito-parietal electrode sites (Fig. 4C). In these two conditions, the amplitude of the effects were highly significant (p<0.01 or p<0.001) from about 200 to 265 msec (Fig. 4C, 2nd and 3rd blocks; mean amplitudes over 215-265 msec: -1.78 µV and -1.20 µV, respectively; see Table 2). The amplitude of the differences remained highly significant up to about 400 msec in the Intentional-age condition (mean over 265-400 msec: -1.85 µV; see Table 2) but was reduced (p<0.05 or p<0.01) in the Intentional-gender condition (mean over 265-400 msec: -0.84 µV). In the Incidental-age condition, the amplitude of the effects did not reach statistical significance at most of the selected posterior electrodes (see Fig. 4C, 1st block; mean amplitude over 215-265 msec: -0.15µV and over 265-400 msec: -0.38 µV; see Table 2).

Figure 4. A. Significant differences were found between about 45 and 90 msec in the three age and gender discrimination conditions. B. A second significant pattern was observed from about 145 to 185 msec with, however, a more restricted effect (in space and time) in the Incidental-age condition. C. A later effect was highly significant from about 200 to 265 msec when age or gender discrimination was explicitly required (Intentional-age and -gender discrimination conditions), this effect lasting up to about 400 msec with the highest amplitudes for age discrimination.

The topography and significance of the effects are displayed at 240 and 400 msec latencies in Figure 3B-D, lines c and d, respectively.

Table 2. Differences between the responses in the No-discrimination condition and the responses in the Incidental-age, Intentional-age and the Intentional-gender discrimination conditions, respectively. Mean amplitude ± SEM (Standard Error of the Mean, in µV) of the differences between the responses in the Incidental-age, Intentional-age and the Intentional-gender discrimination tasks, respectively, and the responses in the No-discrimination task, averaged in time and in space over the periods and the electrode sites as indicated at the top of each column, and compared against zero (Student’s t-tests). *** p<0.001, ** p<0.01, ( ** ) p<0.02, and * p<0.05.
	ERP time periods analyzed
	45-90 msec	145-185 msec	215-265 msec	265-400 msec
Electrode sites	F3-Fz-F4-F8-Cz-C4-T4-TP4-MA2	F3-Fz-F4-C3-Cz-C4-CP1-Pz-CP2	T5-P13-O1-IMA-Iz-IMb-O2-P24-T6
Amplitude of the effects (µV) Incidental-age Intentional-age Intentional-gender	-0.35 ± 0.16 * -0.52 ± 0.13 * -0.49 ± 0.13	0.81 ± 0.26 0.43 ± 0.29 0.87 ± 0.31	-0.15 ± 0.24 -1.78 ± 0.28 * -1.20 ± 0.29 *	-0.38 ± 0.26 -1.85 ± 0.31 * -0.84 ± 0.30 ()

The topographies of the Intentional-age and -gender discrimination effects between 215 and 265 msec latency were further analyzed with two objectives: firstly, since the effects were the largest at posterior scalp sites, they were compared with the topography of the N170 component in the No-discrimination condition to test whether they could be generated within the same brain structures; secondly, they were compared between each others to test whether they could result from the same brain processes. To this end, we computed the interactions between the factors electrode (M1, M2, IMA, IMb, O1, O2, T5, T6) and type of task in a series of two-way ANOVAs on normalized data (McCarthy and Wood, 1985). In two first analyses, we contrasted the mean amplitude of the discrimination effects (Intentional-age and Intentional-gender, respectively) within 215-265 msec with the mean amplitude of the N170 component in the No-discrimination condition (130-170 msec).

In both cases, significant interactions between the two factors were found (age discrimination: F 4, 66 = 14.53, p<0.001, GG epsilon = 0.55; gender discrimination: F 4, 72 = 8.51, p<0.001, GG epsilon = 0.60), indicating that the topographies of both age and gender discrimination effects differed from that of the N170. In a subsequent ANOVA, we found no significant interaction between the electrode and type of task factors comparing the effects of the Intentional-age task with the effects of the Intentional-gender task, suggesting that the scalp topographies of the Intentional-age and -gender discrimination effects did not differ.