Abstract: PURPOSE: Our conscious perception of the world is not an instantaneous moment-by-moment construction, but rather the information subsequent in time seems to affect the percept of the prior event, which was known as postdictive effect. This effect has traditionally been studied in the field of perception. However, a recent study even reported this postdictive effect in decision making, by showing that participants were more likely than chance to selected a certain option when a stimulus was presented soon after the perceived time of choice. The main purpose of the present study sought to directly test the underlying mechanism of this newly discovered postdictive effect.
METHODS: We proposed that attention might be the cause of this effect and conducted two experiments to test this hypothesis. In Experiment 1, participants were shown two circles and were asked to quickly choose one of them mentally. After a variable delay, one of circles turned red, and the other turned another different color, so as to eliminate attentional bias to any of two circles. Participants were then asked to indicate whether they had chosen the circle that turned red. Experiment 2 was identical to Experiment 1 except that attention was directly manipulated by using a spatial cue.
RESULTS: Experiment 1 showed that participants no longer preferred to choose the red circle (i.e., the postdictive effect disappeared) when the attentional bias to the red circle was eliminated. However, when participants' attention was oriented to a certain circle by a cue, their probability of reporting having chosen that circle increased, indicating a postdictive effect on choice.
CONCLUSIONS: These findings suggest that attention plays a crucial role in producing this postdicted choice effect.

Key words: postdictive effect, decision making, attention