Pigeons' preference for variable-interval water reinforcement under widely varied water budgets.

Scientists gave pigeons two water schedules. One gave water every 30 seconds like clockwork. The other gave water every 30 seconds on average, but the wait could be 5 seconds or 60 seconds.

They ran this choice test three ways: normal daily water, half ration, and double ration. The birds picked which schedule they wanted by pecking colored keys.

No matter how much water the birds got that day, they still picked the unpredictable schedule about a large share of the time. Thirsty, water-loaded, or just right—the preference stayed the same.

This shows the variable-interval schedule itself, not the birds’ need state, drove the choice.

MacNaul et al. (2021) found that people’s item choices drift after 8–30 days, so you must re-check preferences often. English et al. (1995) flips that idea: when the reinforcer is a schedule of water, the preference is rock-steady across big motivational swings.

Bigwood et al. (2026) showed that slowing down and adding smiles helps adults with dementia pick items. The pigeon study does the opposite—no extra supports—yet the schedule preference still wins, hinting that schedule effects may be even more robust than item effects.

Rojahn et al. (1994) compared paired vs. group stimulus presentations. Both papers use side-by-side choice methods, but A et al. traded items for schedules, extending the same logic to timing rather than toys.

If your client’s reinforcer loses power, check the schedule before you swap the item. A variable-interval delivery can keep a weak reinforcer strong even when the client is tired, hungry, or satiated. Try thinning to VI 30s on praise or bubbles next week—you may not need new toys.