Varying the temporal placement of a drinking opportunity in a fixed-interval schedule.

Johnson et al. (1994) worked with rats on a fixed-interval 60-second food schedule.

They gave the rats a 5-second chance to drink water at different spots in the interval.

The water probe could pop up early, middle, or right before the next food pellet.

Rats drank less water when the probe came late in the interval.

Lever-pressing patterns changed too—late probes made the usual scallop shape wobble.

Early probes barely touched drinking or pressing, but late probes cut both.

Anger et al. (1976) showed monkeys drink most at 120-second intervals. Johnson et al. (1994) zooms in to show even within one interval, timing still matters.

Davison et al. (1991) found past schedule history can mess up the scallop. Johnson et al. (1994) adds that just dropping a water probe late can do the same thing.

Castilla et al. (2013) later showed hungry rats drink more overall. Johnson et al. (1994) shows that even if the rat is hungry, a probe near food time still cuts drinking.

If you give a client water breaks during DTT or classroom schedules, watch the clock. A drink offered right before the next reinforcer may be refused or rushed. Slide the break earlier to keep both drinking and task behavior steady.