Choice, relative reinforcer duration, and the changeover ratio.

Pigeons pecked two keys for food. One key gave short feed access, the other gave long feed access. A fixed-ratio four changeover rule meant birds had to switch keys four times before the next reinforcer could start. The team varied the size of this changeover requirement to see how it shaped preference.

The setup is a straight laboratory test of basic choice mechanics. No children, no clinic, just birds and grain.

Response rates on each key overmatched the duration ratio. If the right key delivered twice as much food time, birds gave it more than twice the pecks. Bigger changeover requirements made this overmatching stronger. Preference level moved up and down with the size of the switch rule.

Burgess et al. (1971) already showed that non-independent variable-ratio schedules send changeover rates through the roof. Durand (1982) keeps the ratio idea but adds reinforcer duration as a second knob, proving both factors work together.

McClannahan et al. (1990) looks like a contradiction at first. They found nonlinear jumps when birds picked between hard forceful ratios and delayed reinforcers. The difference is the added delay and effort. Once those extra costs enter the picture, choice no longer follows a simple duration line.

Bensemann et al. (2015) widened the test to four alternatives and still saw orderly preference under steady-state conditions. Their constant-ratio rule lines up with M’s duration finding: when the environment holds still, choice stays predictable.

If you run concurrent schedules in a classroom or vocational task, remember that two levers are always in play: how rich each side is and how easy it is to switch. Shorten switch requirements and you may see stronger preference for the richer side. Add response effort or long delays and the neat duration match can break down. Test both variables before you lock in a treatment plan.