An investigation of the differential-outcomes effect within sessions.
Mixing reinforcer sizes within one session lifts accuracy on delayed matching tasks.
01Research in Context
What this study did
The team worked with pigeons in a lab.
Birds had to pick the correct key after a short delay.
Some correct choices earned 2-s grain. Other correct choices earned 6-s grain.
Wrong picks gave no food.
The same bird saw both short and long rewards within one session.
What they found
Pigeons made fewer errors when the two correct responses led to different grain times.
Accuracy dropped when every correct response gave the same amount of food.
Varying reinforcer size inside the session sharpened the birds’ memory.
How this fits with other research
Kohlenberg et al. (1976) showed that different response rules on sample keys also speed learning. The new study adds that different payoff sizes can help even after the task is learned.
Northup et al. (1991) boosted accuracy by adding a distractor key during training. Dougherty et al. (1994) got the same lift by only changing reward length, no extra cues needed.
Santos et al. (2019) found that uneven reward rates within a session can bias timing choices. Together these papers warn us: any reward pattern we set can push behavior in ways we might not expect.
Why it matters
You can make memory tasks easier by pairing each correct response with its own reinforcer size or type. In practice, give the bigger edible for harder discriminations and a smaller one for easier trials within the same lesson. This tiny tweak costs nothing and can cut errors without extra prompts or drills.
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02At a glance
03Original abstract
The differential-outcomes effect is manifest as more accurate performance of a delayed conditional discrimination when alternative choice responses are followed by different reinforcers than when they are followed by the same reinforcer. In Experiment 1, a differential-outcomes effect was demonstrated within sessions by signaling the duration of food access for correct responses with stimuli appearing in conjunction with the sample stimuli. The delayed matching-to-sample performance of 5 pigeons was more accurate when green choice responses (matching a green sample) were followed by 3.5-s food access and red choice responses (matching a red sample) were followed by 0.5-s food access (different-outcome trials) than when the correct choice responses were both followed by 1.5-s reinforcers (same-outcome trials). In Experiment 2, the acquisition of this differential-outcomes effect was characterized by a progressive decrease in rate of forgetting on different-outcome trials and no change in rate of forgetting on same-outcome trials. In addition, accuracy at the shortest delay intervals for both different-outcome and same-outcome trials increased over acquisition, but to a greater extent for different-outcome trials. These data suggest that both memorial and attentional (time-dependent and time-independent) factors contribute to the differential-outcomes effect.
Journal of the experimental analysis of behavior, 1994 · doi:10.1901/jeab.1994.61-389