Control of schedule-induced polydipsia: type, size, and spacing of meals.

Smith (1967) worked with rats on fixed-time food schedules. The team changed three things at once: food type (dry pellets vs. liquid diet), portion size, and the minutes between deliveries.

They watched how much water the rats drank after each bite. The goal was to see which combo creates the strongest schedule-induced polydipsia — the extra drinking that pops up when food arrives on a clock.

Smaller portions and longer waits made the rats drink more, even when the 'food' was already a liquid diet. Dry pellets still triggered the most chugging, but liquid meals also produced clear polydipsia.

Tightening the portion or stretching the interval acted like a dial: turn it one way and drinking surges; turn it back and the behavior fades.

Falk (1966) had already shown that longer fixed-interval schedules alone ramp up polydipsia. The 1967 paper keeps those same intervals and adds food-size and type knobs, giving you a fuller dashboard.

Blackman (1970) later repeated the core effect with both FR and FT schedules, proving the interval — not accidental reinforcement — drives the drinking. Together the three studies draw a straight line: time between bites is the main engine; portion size is the gas pedal.

Bacon-Prue et al. (1980) seemed to clash by using salty liquid food instead of dry pellets. Their rats still overdrank, but only when the liquid was salted. The studies don’t contradict; they show that both portion timing AND taste intensity can spark the same adjunctive pattern.

If you run pauses between reinforcers during therapy, watch for extra sipping, cup grabbing, or other ‘filler’ behaviors. Shrink the portion or lengthen the wait and these side behaviors can explode, even with smoothies or yogurt. Use larger bites or shorter intervals to keep the session focused and reduce accidental polydipsia.