Tone onset and normal tone offset in Nd tasks are formally similar to the S1 and S2 events in a CNV task requiring perceptual discrimination (tone duration) for designated tones. If the Nd thus reflects more than mere stimulus selection, increasing the duration of all tones should lengthen the Nd wave. Eight subjects participated to three Nd tasks, with short tones of 50, 150, and 300 msec, respectively. Mean amplitude difference (Nd) between relevant and distracter tones was measured over consecutive 50-msec time windows from 75 to 370 msec. The Nd was significant at C3, Cz, and C4 from the 125- to 170- to the 275- to 320-msec windows, with a significant tone duration effect only for the 225- to 270-msec time slice, with no sign of extended Nd with longer tones. Although this questions existing views of the Nd, it does not particularly agree with the Nd-as- compressed-CNV hypothesis.