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Behavior and events distributed in time can serve as markers that signal delays to future events. The majority of timing research has focused on how behavior changes as the time to some event, usually food availability, decreases. The primary objective of the two experiments presented here was to assess how behavior changes as time passes between two time markers when the first time marker was manipulated but the second, food delivery, was held constant. Pigeons were exposed to fixed-interval, response-initiated fixed-interval, and signaled response-initiated fixed-interval 15- and 30-s schedules of reinforcement. In Experiment 1, first-response latencies were systematically shorter in the signaled response-initiated schedules than response-initiated schedules, suggesting that the first response was a more effective time marker when it was signaled. In Experiment 2, responding in no-food (i.e. 'peak') trials indicated that timing accuracy was equivalent in the three schedule types. Compared to fixed interval schedules, timing precision was reduced in the signaled response-initiated schedules and was lowest in response-initiated schedules. Results from Experiments 1 and 2 coupled with previous research suggest that the overall 'informativeness' of a time marker relative to other events and behaviors in the environment may determine its efficacy. [ABSTRACT FROM AUTHOR]