Preference for mixed-interval versus fixed-interval schedules.
Pigeons follow the matching law when choosing between mixed and fixed intervals, but only under two-option rules.
01Research in Context
What this study did
Scientists let pigeons pick between two keys. One key led to a fixed-interval schedule. The other led to a mixed-interval schedule.
Birds first pecked an initial link. Their peck rates showed which terminal link they liked more.
What they found
The birds’ pecks matched the reward rates after the data were cubed. This means the matching law still works when the choice is between mixed and fixed intervals.
How this fits with other research
Catania (1972) ran the same birds again and got the same cubic fit. Adding more component intervals did not change the choice.
Catania et al. (1974) later added a third key. Matching broke down with three options. The simple two-key rule no longer held.
Parrott (1984) showed the same intervals can flip preference if the trial ends differently. Cubic math is useful, but session rules still matter.
Why it matters
When you build token or chain schedules, keep the choice simple. Two clear paths track reward rates well. Add a third option or change how the reward ends and the math shifts. Start with two choices and test before you expand.
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02At a glance
03Original abstract
Pigeons were trained on a two-link concurrent chain schedule in which responses on two keys were reinforced according to independent variable-interval schedules by the production of a change in key color. Further responses on the key on which the stimulus change had been produced gave a single food reinforcement and a return to concurrent variable-interval conditions. On one key the terminal link was a two-valued mixed-interval schedule, while on the other, the terminal link was a fixed-interval schedule. When the mixed-interval values were kept constant and the fixed-interval values varied, relative response rates in the initial concurrent links matched relative reinforcement rates in the terminal links when these were computed from cubic transformations of the reciprocals of the intervals comprising the terminal link schedules.
Journal of the experimental analysis of behavior, 1969 · doi:10.1901/jeab.1969.12-247