Discriminability of fixed-ratio schedules for pigeons: effects of payoff values.
Reinforcement size or chance can pull choices toward one option without making the stimulus easier to see.
01Research in Context
What this study did
Fields (1978) worked with pigeons in a signal-detection box. The birds pecked left or right depending on which light they saw.
The team changed only the payoff. Sometimes a correct left peck paid more grain. Sometimes a correct right peck did. The birds never got better or worse at seeing the lights.
What they found
When the payoff favored one side, the birds simply pecked that side more. Their bias shifted, but their ability to tell the lights apart stayed the same.
In plain words: bigger reward pulls responses, not better vision.
How this fits with other research
Gentry et al. (1980) ran almost the same test and got the same split: reward rate moves bias, not sensitivity. The finding is reliable.
Malouff et al. (1985) extended the idea to free-operant schedules. When the lights were easy to tell apart, reinforcer rate inside each schedule steered bias. When the lights were hard, the chance of seeing each schedule drove bias instead.
Brinton et al. (1996) added one more layer: fast pigeon choices showed bigger bias shifts than slow ones. Same payoff rule, but speed matters.
Why it matters
You can tilt a client’s preference without teaching new discrimination. If you want more correct manding to one peer, give that peer the better reinforcer. The child will shift toward that peer, yet still tell the peers apart. Use payoff to bias, then teach accuracy later.
Want CEUs on This Topic?
The ABA Clubhouse has 60+ free CEUs — live every Wednesday. Ethics, supervision & clinical topics.
Join Free →Keep the S+ the same, but deliver the reinforcer 100% on the target side and 30% on the other for one session; count if responses shift before you retrain the discrimination.
02At a glance
03Original abstract
Three pigeons, previously trained to discriminate different numbers of responses (fixed ratios), were tested under different reinforcement contingencies (payoff matrices) at two levels of sensitivity. For one subject, relative reinforcement magnitude was varied-at first, across sessions and then, at midsession by reversing values-without exteroceptive cues. For another, relative reinforcement magnitude and/or probability was varied every 50 trials with cues by correlating different payoff matrices with different key colors. For the third subject, relative reinforcement probability was varied more frequently with cues-in the limit, at random-to demonstrate stimulus control of response bias on a trial-by-trial basis. A signal-detection analysis showed that bias changed with payoffs, for as many as seven different matrices, while sensitivity remained unchanged. The obtained functions (receiver operating characteristics) were similar under different payoff conditions, which suggests that a single mechanism controls bias. However, they differed enough in slope to require a relatively complex account (e.g., the general Gaussian model of detection theory).
Journal of the experimental analysis of behavior, 1978 · doi:10.1901/jeab.1978.30-69