Figure 1.

Experimental setup and basic countermanding findings. A, Graphical depiction of the three trial types. During the preparation of the test saccade, which occurs after a sequence of three to six saccades, a stop signal could be given (color change of the fixation point). At various times, a green vertical bar was flashed, which subjects had to localize in space after the trial was ended (using mouse control). Go trials (green) are trials without a stop signal; noncancelled trials (in blue) are trials with a stop signal, but a saccade was made; cancelled trials (in red) are trials with a stop trial during which the saccade was successfully inhibited. B, SRT of a representative subject subdivided by the saccade-sequence length and trial type. SRTs of the noncancelled trials are significantly lower than those of the go trials (p < 0.05). C, Inhibition functions subdivided by sequence length for the same subject. D, SSRT does not vary systematically with sequence length (p > 0.05).