Concurrent assessment of schedule and intensity control across successive discriminations.
Shrink stimulus differences slowly so the learner stays tuned to the cue, not just the pay-off.
01Research in Context
What this study did
Weisman et al. (1975) worked with chinchillas on an auditory task.
The animals chose between two levers when tones varied in loudness.
Researchers made the tone difference smaller across phases to see what controlled the choice: the reinforcement schedule or the sound intensity.
What they found
As the tone difference shrank, schedule control grew.
At the same time, intensity control faded.
The animals’ hearing threshold sat near two decibels, showing the task truly became harder.
How this fits with other research
Kelly et al. (1970) showed the same fading idea works with pigeons.
They slowly dimmed a bright light so an overshadowed sound could take control, matching the takeaway here.
Leigland (1987) looked richer concurrent schedules and saw flatter discrimination curves, extending the trade-off into visual tasks.
Newman et al. (1991) later proved the rule is systematic: the steeper the stimulus contrast, the more reinforcer ratios steer choice.
Why it matters
When you fade stimuli for a learner, move in tiny steps.
Each small jump keeps stimulus control alive while the reinforcement schedule stays strong.
If you go too fast, schedule control takes over and the learner may stop noticing the cue you want.
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02At a glance
03Original abstract
Two chinchillas were trained on a series of two-valued auditory intensity discriminations. Lever presses were reinforced when no tone was present and not reinforced in the presence of a four-kiloHertz tone. The intensity of the nonreinforced tone was successively decreased, increasing the difficulty of the discrimination, until differential responding resembled that on a mixed schedule (no-tone-no-tone). Response data were partitioned in such a way as to provide a continuing assessment of the relative amounts of control exerted by the reinforcement schedule and the sound intensity, respectively. Control by reinforcement density was a direct function of discrimination difficulty, whereas the control exerted by intensity was inversely related to difficulty. For these chinchillas, the absolute threshold value obtained at four kiloHertz was about two decibels referenced to 20 microNewtons per meter squared.
Journal of the experimental analysis of behavior, 1975 · doi:10.1901/jeab.1975.23-247