Discrete and continuous measures of dimensional stimulus control.
Continuous rate recording catches stimulus-control shifts that discrete counts miss, but only under free-operant conditions.
01Research in Context
What this study did
The team used a free-operant setup. Pigeons could peck any time.
A key peck paid off only when a light flickered at one rate.
They compared two ways to score the birds: counting each discrete choice or logging the continuous rate of pecks.
What they found
Both scoring methods showed the same clear picture.
Continuous rate caught the shift in pecking just as well as counting single choices.
Free-operant work gave a strong dimensional contrast effect; discrete trials did not.
How this fits with other research
Pear et al. (1971) and Aragona et al. (1975) saw contrast in rats under multiple schedules, but the effect faded. The 1989 study shows the same phenomenon can last when you stretch a stimulus dimension instead of switching schedules.
Fujimaki et al. (2025) got robust resurgence with discrete trials, which looks like a clash. The difference is the behavior: resurgence is the return of an old response, while dimensional contrast is a shift along a flicker-rate gradient. One works in trials, the other needs free pecking.
Logue (1983) and Jones et al. (1998) also pushed continuous measures in concurrent schedules. Together they build a rule: when you need to see fine shifts in stimulus control, keep the clock running instead of stopping at one choice.
Why it matters
If you run free-operant preference or discrimination probes, log responses every second, not just the final pick. Continuous data can reveal a weak stimulus control signal that trial counts hide. Next time a learner shows flat discrete-trial results, try a free-operant stretch and watch the rate curve—you might find the gradient was there all along.
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Join Free →During your next free-operant preference assessment, tally responses every 5 s and graph the rate curve instead of just the final choice.
02At a glance
03Original abstract
In two sets of experiments, we examined dimensional stimulus control of pigeons' responses to a visual flicker-rate continuum. In the first experiment, responses to a single key were reinforced periodically during stimuli from one half of the stimulus continuum, and responses during other stimuli were extinguished. In the second experiment, two response keys were simultaneously available, with reinforcement for each response alternative associated with different halves of the stimulus continuum. Conditions of the second experiment involved either free-operant or discrete-trial stimulus presentations. Results from these experiments show that positive dimensional contrast appeared in discrimination tasks with one or two response alternatives, but only with free-operant procedures. In addition, discrimination between stimulus classes established by differential reinforcement was assessed as accurately by continuous rate measures as by discrete response choice in the two-alternative situation. The general implication of these experiments is that response rate measures, when properly applied, may reveal sources of variation within stimulus classes, such as dimensional contrast, that are not evident with discrete measures.
Journal of the experimental analysis of behavior, 1989 · doi:10.1901/jeab.1989.51-199