Effect of reinforcer magnitude on performance maintained by progressive-ratio schedules.
Double the reinforcer size and you can double the work before the learner quits.
01Research in Context
What this study did
Tyrer et al. (2009) worked with eight lab rats pressing a lever for sugar water. They tested three volumes: 0.05 ml, 0.1 ml, and 0.2 ml per press.
The schedule got harder after each reward. The first reinforcer cost one press, the next cost two, then four, eight, and so on. They recorded how many rewards the rat earned before quitting.
What they found
Bigger drinks kept the rats going longer. The 0.2 ml volume pushed the average breakpoint to 48 rewards; the 0.05 ml volume stopped at 24.
The math backed it up. Larger volume raised the 'incentive value' parameter and made the response-rate curve drop off more steeply after the peak.
How this fits with other research
Szempruch et al. (1993) predicted this. Their unit-price rule says cost ÷ size predicts behavior. Tyrer et al. (2009) show the rule works when you hold cost and double the size.
Duker et al. (1996) asked kids to pick toys first. High-preference items later worked harder as reinforcers. The rat study extends the idea: once you know the preferred size, you can scale it to magnify effect.
Schulingkamp et al. (2023) looked at social reinforcers and found familiarity did not change demand. Tyrer et al. (2009) show that for edible reinforcers magnitude does matter. Together they tell us to tweak the edible, not the social, when we want more output.
Why it matters
Next time a client stalls on a task, try doubling the size of the edible or the seconds of screen time before you raise the response requirement. One quick magnitude jump can restore momentum and save you from re-planning the whole program.
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02At a glance
03Original abstract
This experiment examined the relationship between reinforcer magnitude and quantitative measures of performance on progressive-ratio schedules. Fifteen rats were trained under a progressive-ratio schedule in seven phases of the experiment in which the volume of a 0.6-M sucrose solution reinforcer was varied within the range 6-300 microl. Overall response rates in successive ratios conformed to a bitonic equation derived from Killeen's (1994) Mathematical Principles of Reinforcement. The "specific activation" parameter, a, which is presumed to reflect the incentive value of the reinforcer, was a monotonically increasing function of reinforcer volume; the "response time" parameter, delta, which defines the minimum response time, increased as a function of reinforcer volume; the "currency" parameter, beta, which is presumed to reflect the coupling of responses to the reinforcer, declined as a function of volume. Running response rate (response rate calculated after exclusion of the postreinforcement pause) decayed monotonically as a function of ratio size; the index of curvature of this function increased as a function of reinforcer volume. Postreinforcement pause increased as a function of ratio size. Estimates of a derived from overall response rates and postreinforcement pauses showed a modest positive correlation across conditions and between animals. Implications of the results for the quantification of reinforcer value and for the use of progressive-ratio schedules in behavioral neuroscience are discussed.
Journal of the experimental analysis of behavior, 2009 · doi:10.1901/jeab.2009.91-75