Illustration of stimuli: The fixation cross was visible throughout a trial.

<p>A pre-cue condition appeared for 67 msec. Conditions a) no cue and b) dual cues of a single luminance were used as baseline conditions for the calculations of derived measures as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030731#pone-0030731-t001" target="_blank">Table 1</a>. Otherwise, either one or two cues of different luminances appeared. A single target as in condition c) could appear on either the left or right side with 50% probability and could be either bright or dim (50% probability each). The target that followed could appear near where the pre-cue had appeared or contralaterally. If two cues appeared as in condition d) then the bright cue would appear on the left side for 50% of these trials. After the cue condition disappeared, a single target followed and could appear near the dim or the bright cue.