Positive behavioral contrast across food and alcohol reinforcers.

Researchers tested how removing one reward changes behavior for another reward.

They used rats working for food pellets and alcohol.

Two setups were used: concurrent schedules where both rewards were available at once, and multiple schedules where rewards alternated in time.

When alcohol was removed, food responses increased strongly in concurrent schedules.

When food was removed, alcohol responses also increased in concurrent schedules.

But in multiple schedules, only food showed this contrast effect - alcohol responses stayed flat.

Rojahn et al. (1994) found money and cigarettes acted independently, supporting K et al.'s finding that food and alcohol can function separately.

Duker et al. (1996) showed reinforcer quality affects allocation, which helps explain why alcohol (a weaker reinforcer) showed less contrast than food.

Landa et al. (2016) successfully used multiple schedules to reduce PECS requests, but K et al. shows multiple schedules might miss contrast effects that concurrent schedules would reveal - an apparent contradiction based on schedule type, not disagreement.

When you assess reinforcer value, use concurrent schedules to catch contrast effects that multiple schedules might hide. If a client stops working for tokens when snacks are removed, try presenting both options together to see the true contrast. This matters for preference assessments and treatment integrity checks.