Stimulus bias in the absence of food reinforcement.

Two pigeons pecked a key under a DRL 20-s schedule. Food came only after 20 seconds passed.

Next, the birds entered extinction. Two key colors alternated. No food ever appeared.

The birds still pecked more on one color than the other. Bias lived on without reinforcement.

Schedule effects do not need food to create uneven responding.

Striefel et al. (1974) saw behavioral contrast even when extinction cut responding to near zero. Both studies show extinction can change behavior without rate suppression.

Mulvaney et al. (1974) linked contrast to autopecking at localized stimuli. Lander (1968) adds that simple color cues also steer choice when food stops.

Kodera et al. (1976) found contrast after errorless training. Together, these papers tell us that stimulus control can swing even when training looks gentle.

Your client may keep preferring one toy, room, or aide after reinforcement ends. Check for leftover stimulus bias before you blame motivation. Swap cues, fade gradually, or add competing stimuli to rebalance responding.