After each stimulus, observers made two different judgements. First, they used a mouse-controlled cursor to indicate the perceived direction of global flow; then, they used a six-point scale to rate their certainty that the stimulus had been signal rather than noise.

Accuracy of judgments of global flow's direction was indexed by the absolute difference between the actual mean direction of flow and the subject's judged direction of flow. Accuracy of judging the direction of global flow differed significantly across age-groups (p<.01), and there was a significant interaction between age group and duration (p<.01). Post-hoc tests showed that accuracy was significantly lower in the 70-81 yr olds, especially at the shortest durations.
