Two choices good, four choices better: For measuring stereoacuity in children, a four-alternative forced-choice paradigm is more efficient than two.

However, we observed a highly significant difference in the duration of the experiment after controlling for age (ANCOVA: F(2,89) = 9.489, p < .001, mean 2-AFC = 206.20 sec, mean 4-AFC = 135.37 sec, Fig 8 ), indicating completing 30 trials in a 4-AFC task takes considerably less time than completing 60 trials in a 2-AFC task even though the average trial duration in the 4-AFC was significantly longer than in the 2-AFC experiment (mean 2-AFC = 3.44 sec, mean 4-AFC = 4.51 sec, ANCOVA: F(2,89) = 4.682, p = .01).

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