Contrast and autoshaping in multiple schedules varying reinforcer rate and duration.
Changing reinforcer rate or duration can create contrast or induction even when autoshaping is ruled out.
01Research in Context
What this study did
Hamilton et al. (1978) worked with pigeons in a lab. They used multiple schedules that changed how often and how long grain was given.
The team wanted to see if contrast or induction would show up. They also checked if autoshaping caused the shifts.
What they found
Half the birds gave more pecks when the other schedule paid less. That is positive contrast.
The other half pecked less when the other schedule paid more. That is positive induction.
Autoshaping did not explain either outcome.
How this fits with other research
Neef et al. (1978) ran a near-copy study the same year. They also saw both contrast and induction in pigeons, but used discrete-trial choice instead of free pecking. The two papers back each other up.
Wesp et al. (1981) later showed contrast even when food came no matter what the bird did. Together with E et al., this tells us contrast can pop up without true operant or Pavlovian contingencies.
Maltz (1981) went further, saying the next schedule in line is what really drives steady-state contrast. E et al. helped spark that sharper view.
Why it matters
If you run multiple schedules with clients, know that rate or duration shifts can push responding up or down in the next component. The change is not just autoshaping. Watch for contrast when reinforcement drops and for induction when it rises. Plan transitions and probe data by component, not just by session.
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02At a glance
03Original abstract
Thirteen master pigeons were exposed to multiple schedules in which reinforcement frequency (Experiment I) or duration (Experiment II) was varied. In Phases 1 and 3 of Experiment I, the values of the first and second components' random-interval schedules were 33 and 99 seconds, respectively. In Phase 2, these values were 99 seconds for both components. In Experiment II, a random-interval 33-second schedule was associated with each component. During Phases 1 and 3, the first and second components had hopper durations of 7.5 and 2.5 seconds respectively. During Phase 2, both components' hopper durations were 2.5 seconds. In each experiment, positive contrast obtained for about half the master subjects. The rest showed a rate increase in both components (positive induction). Each master subject's key colors and reinforcers were synchronously presented on a response-independent basis to a yoked control. Richer component key-pecking occurred during each experiment's Phases 1 and 3 among half these subjects. However, none responded during the contrast condition (unchanged component of each experiment's Phase 2). From this it is inferred that autoshaping did not contribute to the contrast and induction findings among master birds. Little evidence of local contrast (highest rate at beginning of richer component) was found in any subject. These data show that (a) contrast can occur independently from autoshaping, (b) contrast assays during equal-valued components may produce induction, (c) local contrast in multiple schedules often does not occur, and (d) differential hopper durations can produce autoshaping and contrast.
Journal of the experimental analysis of behavior, 1978 · doi:10.1901/jeab.1978.30-107