Signal probability, reinforcement and signal detection.
Keep reinforcer rates equal across choices to stop unwanted response bias during conditional-discrimination training.
01Research in Context
What this study did
Researchers worked with pigeons in a signal-detection game. Birds pecked left or right when lights were bright or dim.
The team changed how often each choice paid off. They kept the light brightness the same. They wanted to see if payoff odds, not the lights, steered the birds’ bias.
What they found
When the left key paid more, birds leaned left even if the light never changed. Their ability to tell bright from dim stayed flat.
Only the bias moved. The authors showed that relative reinforcement, not stimulus probability, controls response bias in detection tasks.
How this fits with other research
Rider et al. (1984) added a delay between the light and the choice. Accuracy dropped fast, yet payoff still ruled bias. The 1979 finding holds even when memory fades.
Panlilio et al. (2000) repeated the payoff trick with adult humans. Again, locked-down reinforcer ratios kept bias clean. The pigeon rule crosses species.
Alsop et al. (1995) found a twist with humans: stimulus probability and payoff shared the steering wheel. People, unlike pigeons, let stimulus odds pull bias too. Same lab game, different species, extra factor.
Why it matters
When you run conditional-discrimination programs, hold reinforcement rates steady across choices. If one correct response pays more, learners will drift toward it even when stimuli stay the same. Check your payoff schedule before you blame poor stimulus control.
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02At a glance
03Original abstract
Five pigeons were trained to detect differences in light intensity. Two stimuli, S1 and S2, differing in intensity, were arranged on the center key of a three-key chamber according to set probabilities. A peck on the center key turned on the two side keys. When S1 was presented on the center key, a peck on the left key was "correct" and when S2 was presented, a peck on the right key was "correct." Correct responses produced reinforcement and incorrect responses produced 3-second blackout. Detection performance was measured under three procedures. The first was a standard signal-detection design in which the probability of S1 was varied and the number of reinforcements obtained for correct responses to S1 was allowed to covary. In the second procedure, the probability of S1 was again varied but the distribution of reinforcements between the two choices was kept equal. In the third procedure, probability of S1 was held constant while the distribution of reinforcements was varied between the two choices. Changes in response bias were a function of variations in the relative reinforcement ratio for the choice responses and not a function of variations in the probability of stimulus presentation. Discriminability remained constant across the three procedures.
Journal of the experimental analysis of behavior, 1979 · doi:10.1901/jeab.1979.32-373