Effects of varying stimulus disparity and the reinforcer ratio in concurrent-schedule and signal-detection procedures.
Stimulus clarity decides how much reinforcer ratios sway choice, and the task type decides the shape of that sway.
01Research in Context
What this study did
The team worked with pigeons in two lab tasks. One task was a simple concurrent schedule: two keys, two reinforcer rates. The other was a signal-detection task: one key had a dim light, one had a bright light.
They changed two things at once. First, they varied the reinforcer ratio, like 9:1 versus 1:9. Second, they varied stimulus disparity, making the lights almost the same or very different. They wanted to see how these two factors mix.
What they found
Reinforcer ratios still guided choice, but the size of the effect depended on how different the stimuli looked. When the lights were easy to tell apart, reinforcer ratios pushed choice around in one pattern. When the lights were hard to tell apart, the same ratios pushed choice in a different pattern.
The pattern also flipped between the concurrent schedule and the signal-detection set-up. Same birds, same ratios, but the task shape mattered.
How this fits with other research
Bryant et al. (1984) first showed that reinforcer schedules alone can bias pigeons in a drug-versus-saline detection task. Newman et al. (1991) asked the next question: does stimulus clarity change that bias? Their answer is yes; low disparity lets reinforcer ratios dominate in new ways.
Landon et al. (2002) later split ratio effects into short-term and long-term pieces. They found that extreme ratios create quick post-reinforcer swings. Newman et al. (1991) did not look at time, so the two papers sit side-by-side: one shows disparity matters, the other shows timing matters.
Roane et al. (2001) moved the idea to humans and swapped stimulus disparity for response disparity. They also found that finer options sharpen discrimination. Together, the bird and human data tell the same story: the clarity of the choice set-up controls how strongly reinforcer ratios bite.
Why it matters
When you build discrimination programs, think about both the reinforcer plan and the stimulus plan. If the S+ and S- look almost alike, reinforcer ratios will steer behavior more than you expect. Make the stimuli obviously different, or watch for unwanted ratio bias. Check your task type too: concurrent schedules and detection tasks may give different looks at the same learner.
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02At a glance
03Original abstract
The present study measured the effects of stimulus and reinforcer variations on pigeons' behavior in two different choice procedures. Two intensities of white light were presented as the stimuli on the main key in a switching-key concurrent schedule and as the sample stimuli in a signal-detection procedure. Under both procedures, the scheduled rate of reinforcement was varied across conditions to produce various ratios of obtained reinforcement. These ratios were obtained for seven pairs of light intensities. In the concurrent schedules, the effects of reinforcer-ratio variations were positively correlated with the physical disparity between the two light intensities. In the signal-detection procedure, changes in the reinforcer ratio produced greater effects on performance when stimulus disparity was very low or very high compared to those found at intermediate levels of stimulus disparity. This discrepancy creates a dilemma for existing behavioral models of signal-detection performance.
Journal of the experimental analysis of behavior, 1991 · doi:10.1901/jeab.1991.56-67