Thresholds for detecting the bend of a chevron pattern were measured with SOA of its two component lines in a range from 0 to 1.5 sec. Duration D and length L of the lines were also varied from 0.01 to 1.5 sec., from 25 to 200 min. of arc, respectively. The results show that the thresholds were almost constant for all Ds in a range of SOA, at least, from 0 to 50-100 msec., and then began to increase rapidly at the SOAs which values depended on Ds. It was also obtained that the thresholds increased as a function of L, and became proportional to L when SOA was 1.5 sec. Simultaneous and successive integrations of the lines may be considered to explain these results.