Pigeon responding in fixed-interval and response-initiated fixed-interval schedules.

Robertson et al. (2013) compared two pigeon schedules side-by-side. One was a plain fixed-interval. The other waited for a peck to start the clock. They tracked how long birds waited, how fast they pecked, and how well they told time.

The goal was to see if asking for a starter peck changed the classic FI scallop.

Birds on the response-initiated schedule pecked more in the first half of the interval. Their pauses were longer and more scattered. Yet both groups learned the clock equally well. The extra peck did not hurt timing, it just front-loaded work.

Glynn (1970) first showed the break-and-run pattern under RIFI. Robertson et al. (2013) now add that the break grows and the run starts sooner, but timing accuracy stays intact.

HEFFERLINE et al. (1963) split the pause with a second lever. E et al. swap the lever for a simple first peck, proving you can keep the measure without extra hardware.

Kono (2017) found longer FIs make peck location drift. E et al. show the same intervals under RIFI make peck timing drift instead. Same schedule, different variable watched.

If you run FI-based token boards or DRL self-control programs, know that adding a starter response raises early work but keeps the clock skill. You can use the starter to build initiation without losing temporal discrimination. Try it next session: ask for one quick response to start a fixed wait time and watch the front-loaded burst appear.