The responses to stimulus change consisting in the choice of maze arm where the brightness was changed between two consecutive trials were studied in an enclosed T maze with varying exposure times and retention intervals. The strength of memory involved in the response-to-change test depended on both variables. Memory acquired in 10 min exposure survived around 25 min, while after 1 min exposure memory decayed in less than 15 min. Under conditions of paucity of memory traces rats relied on their directional preferences.