Concurrent schedules: Spatial separation of response alternatives.

The team set up two levers side by side. Each lever paid off on its own VI 20-s schedule.

They then slid the levers farther apart in steps. The question: does distance change how often the subject switches between them?

When the levers were almost touching, the subject hopped back and forth often.

As the gap grew, switching dropped. The animal soon stayed on the richer side almost all the time.

White (1979) saw the same drop in switching, but they did it by raising the number of responses needed to change over. Both papers show fewer changeovers create stronger preference for the rich schedule.

Jarrold et al. (1994) moved the idea into a classroom token system. Kids under-matched unless the teacher added extra cues. Their results echo H et al.: if you make the choice harder to see or reach, you must add supports.

McLean et al. (2018) flipped reinforcer ratios every day. Rats still matched inside each session, but their sensitivity faded across days. Together with H et al., this warns us that both space and time can blunt matching.

In therapy rooms, keep two task stations close while a learner is choosing. If you must spread them out, add clear cues or brief change-over delays so the learner still samples both sides. Watch for "sticky" behavior on the richer side; it may mean the layout, not the reinforcer rate, is driving the choice.