Effects of the age and gender discrimination tasks on the N170 component

The bilateral occipito-temporal distribution of the N170 component elicited by non-target faces in the No-discrimination condition is illustrated in Figure 3A at its peak latency (150 msec). Although the peak amplitude of N170 tended to be larger on the right (T6) than on the left (T5) hemiscalp in all conditions (on average -4.39 µV vs -3.16 µV), the differences did not reach statistical significance when contrasting the mean potential value over ±20 msec around the peak at IMA, M1, T5 and IMb, M2, T6 (on average -1.69 µV and -1.14 µV, respectively, F 2, 40 = 1.79, GG epsilon = 0.78, p<0.17; see Methods and Figure 2).

A two-way ANOVA performed on the N170 peak latency showed no effect of hemisphere but revealed a significant effect of the type of task (F 3, 45 = 15.68, GG epsilon = 0.88, p<0.001) that was due to a slightly later peak latency in the Incidental-age discrimination task (155 msec) than in the three other tasks (152 msec in each of them).

No significant interaction was found between the type of task and hemisphere factors on N170 amplitude or latency.

Figure 2. Grand average ERPs elicited by non-target face stimuli at selective anterior and posterior electrodes in the four visual discrimination tasks (No-discrimination, Incidental-age, Intentional-age and Intentional-gender discrimination). The shaded rectangles indicate the time periods when the responses in either age or gender discrimination task differ from that observed in the No-discrimination task. The N170 component is indicated at T5/T6 electrodes where it is maximum.