Stock optimizing in choice when a token deposit is the operant.
A simple token-return event can drive more responding than a higher pay rate.
01Research in Context
What this study did
Lab monkeys faced two slot machines. One kept any tokens they earned. The other gave the tokens back after each play.
The team changed the pay-off schedules. Sometimes the keep-slot paid more often. Sometimes the return-slot did. The question: which would the monkeys choose?
What they found
Even when the keep-slot paid better, the monkeys still picked the return-slot most of the time.
They were not chasing the highest pay rate. They were chasing the sight of tokens coming back. The return mechanism itself acted like extra reinforcement.
How this fits with other research
Leca et al. (2021) watched wild monkeys swap stolen tokens with tourists for food. The animals got better at the game as they aged, showing token economies can grow outside the lab. Weiss et al. (2001) takes that idea inside and proves the return step is the hook.
Mellitz et al. (1983) showed pigeons pick the option with the highest chance of food right now. That rule would tell the monkeys to favor the richer slot, but they did not. The token-return effect overrides simple momentary maximizing.
Richman et al. (2001) found rats pile up more pellets when they must walk between earn and collect levers. Separating gain from access boosts accumulation. The monkey study flips this: giving tokens back right away also boosts responding. Both papers show that how you deliver the reinforcer can matter more than how much you deliver.
Why it matters
Token boards, point sheets, and penny boards are common in classrooms and clinics. This study warns that the moment you hand the token back can be as powerful as the item the client buys later. Try adding an immediate "token return" praise step—drop the chip into their cup with a splash—before they trade in. You may see more work for the same payoff.
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02At a glance
03Original abstract
Each of 2 monkeys typically earned their daily food ration by depositing tokens in one of two slots. Tokens deposited in one slot dropped into a bin where they were kept (token kept). Deposits to a second slot dropped into a bin where they could be obtained again (token returned). In Experiment 1, a fixed-ratio (FR) 5 schedule that provided two food pellets was associated with each slot. Both monkeys preferred the token-returned slot. In Experiment 2, both subjects chose between unequal FR schedules with the token-returned slot always associated with the leaner schedule. When the FRs were 2 versus 3 and 2 versus 6, preferences were maintained for the token-returned slot; however, when the ratios were 2 versus 12, preference shifted to the token-kept slot. In Experiment 3, both monkeys chose between equal-valued concurrent variable-interval variable-interval schedules. Both monkeys preferred the slot that returned tokens. In Experiment 4, both monkeys chose between FRs that typically differed in size by a factor of 10. Both monkeys preferred the FR schedule that provided more food per trial. These data show that monkeys will choose so as to increase the number of reinforcers earned (stock optimizing) even when this preference reduces the rate of reinforcement (all reinforcers divided by session time).
Journal of the experimental analysis of behavior, 2001 · doi:10.1901/jeab.2001.76-245