Time's arrow and pupillary response.

The psychological arrow of time refers to our experience of the forward temporal progression of all natural processes. To investigate whether and how time's arrow is mentally coded in individual everyday events, a relatedness judgment task was used. The items each consisted of a verb (probe) and an adjective or participle (target). The temporal orientation between probe and target was varied either corresponding to the chronological orientation (e.g., shrinking-small) or corresponding to the reverse orientation (e.g., shrinking-large). Reaction times, error rates, and pupillary responses were recorded. Chronological items were processed faster than reverse items. These findings suggest that time's arrow is mentally coded in single everyday events. Pupil dilation and results of principal component analyses suggest top-down influences in the processing of temporally related items.