A response-initiated fixed-interval schedule of reinforcement.

Glynn (1970) worked with pigeons on a new twist of the fixed-interval schedule. The bird had to peck once to start the timer. After the set time passed, the next peck produced food.

The schedule is called response-initiated fixed-interval (RIFI). The single peck starts the clock. All later pecks wait until the interval ends.

After each food delivery the bird paused. The pause length matched the interval time. A 60-second schedule produced about a 60-second pause.

When the pause ended the pigeon burst into rapid pecking. This break-and-run pattern appeared every cycle.

HEFFERLINE et al. (1963) first showed the same schedule in rats and monkeys. They split the pause into two parts: the wait to start the timer and the wait for food. Glynn (1970) confirmed the pattern in pigeons.

Robertson et al. (2013) later compared standard FI and RIFI side by side. RIFI made the pause longer and more variable, yet the birds still tracked time just as well. The 1970 finding still holds, but the newer data show costs in variability.

Glynn (1970) also tested whether a response was needed after the interval. The pause stayed the same whether or not a final peck was required. This supports the idea that pause length is controlled by the time signal, not by the response contingency.

If you run fixed-interval programs, know that requiring a single response to start the clock will lengthen the post-reinforcement pause. Clients may wait longer before working. Check for this pattern in your data. If the pause becomes too long, switch back to a standard FI or add prompts to shorten the break.