Positive and negative contrast as a function of component duration for key pecking and treadle pressing.

McSweeney (1982) ran pigeons on a two-part schedule.

Each part gave grain for either key pecks or treadle presses.

The team kept the pay rate the same but made each part last 30, 60, or 120 seconds.

They watched how hard the birds worked when the rules suddenly changed.

Key pecking showed strong contrast: short parts made the burst bigger, long parts made it smaller.

Treadle pressing did the opposite: long parts gave the bigger burst.

Same pay, same birds, but the body part used flipped the result.

Carmichael et al. (1999) also played with schedule parts and saw no effect from delay length—only pay rate mattered for choice.

Their birds picked with their beaks, so the body-topography rule in McSweeney (1982) fits: beak work tracks rate, foot work tracks time.

Grosch et al. (1981) found humans ramped their finger taps to match rising pay.

That study used long cycles, matching the treadle pattern in McSweeney (1982): longer parts let foot or finger responses ride the wave.

Together the three papers say: check what body part the learner uses before you pick your schedule length.

If you run a two-part program—say, table work then play—watch the response form.

Hand touches may need short parts to see a big burst; foot steps or whole-body moves may need long parts.

Try both lengths, measure, and keep the one that gives you the clearest contrast.