Time ’ s Arrow and Pupil Response 1 Time ’ s Arrow and Pupillary Response

The psychological arrow of time refers to our experience of the relentless 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). In addition, the interval between probe and target presentation was varied (SOA: 250 ms vs. 1,000 ms). Reaction times, error rates, and pupillary responses were recorded. For both SOA-conditions, chronological items were processed faster than reverse items. These findings suggest that time’s arrow is mentally coded in single everyday events. Furthermore, pupil dilation and results of principal component analyses on mean pupillary responses suggest topdown influences in the processing of temporally related probe target pairs.