Two choices good, four choices better: For measuring stereoacuity in children, a four-alternative forced-choice paradigm is more efficient than two
Fig 3
Full screen examples of the stimuli in the 2-AFC and the 4-AFC task.
Panel (A) shows a practice trial of the 2-AFC task with line-interleaved elliptic dots. Right side shows the target stimulus: a squared patch standing out in depth from the background. Left side shows the distractor stimulus with only one depth plane. In addition to the disparity difference the target area is also presented in red. This colour/luminance cue is removed after the practice trials. (B) Example of the 4-AFC task with the target stimulus in the right upper quadrant. See dimensions in the main text.