Preference for qualitatively different reinforcers.

Researchers let pigeons peck two keys. One key gave food pellets. The other gave mild brain stimulation.

Both rewards were set on the same VI schedule. The birds could switch keys at any time.

The birds spread their pecks the same way no matter which reward they were working for.

The matching law still fit. Different rewards behaved like different flavors of the same thing.

Smith et al. (1997) later asked children with autism to pick one top toy or a rotating box of so-so toys. About half the kids chose the variety, showing the same unified preference rule in people.

Norris et al. (2024) used the same logic to rank the social, escape, and sensory pay-offs that keep problem behavior alive. One quick choice test showed which reinforcer really drove each child.

Allan et al. (1994) swapped reward type for reward reliability. Pigeons still followed the matching law, proving the rule holds across quality, variety, and certainty.

You can treat any reinforcer—cookies, praise, screen time, break from work—as points on the same scale. Run a quick concurrent choice test, graph the split, and you have a single preference score you can trust. No need to build separate systems for edible, social, or sensory rewards.