Varying temporal placement of an added stimulus in a fixed-interval schedule.

The team put pigeons on a three-minute fixed-interval schedule. A six-second green light popped up at different spots inside each interval.

They moved the light to the start, middle, or end. Then they drew response-rate curves to see how timing changed the birds' pecking.

Early light made a steep scallop: birds waited, then burst. Late light flattened the curve: birds pecked steadily.

The same six-second cue acted like a different signal just because its clock position changed.

White (1995) extends this idea. Instead of three spots, G showed stimulus control fades the longer a component runs. Together the papers map both discrete placement points and the smooth decay curve.

Sherwell et al. (2014) also extend the 1966 work. They proved brief added cues help animals notice when reinforcer odds flip, moving the finding from response pattern to better choice accuracy.

Killeen (2023) wraps all these facts into one math frame. The review says richer schedules build momentum; timing cues like the 1966 light are levers you can place to speed or brake that momentum.

If you run FI schedules or DRO/DRL with clients, drop a brief visual or sound at the spot where you want responding to change. Early cues build wait time; late cues keep steady work. Map the curve once, then reuse the cue placement that gives the pattern you need.