Effects of changeover delay on response allocation during probe tests.
Old changeover delays can make a stimulus look better even after the delay is gone.
01Research in Context
What this study did
The team worked with six pigeons in a long chamber. Two keys sat on the front wall.
Each key paid food on its own variable-interval schedule. The birds could hop back and forth.
Some sessions added a 1-second changeover delay. Others added 10 seconds. Later the birds got probe tests with no delay at all.
What they found
When the delay was gone, the birds still picked the key that used to have the 10-second wait.
Equal food was now on both keys, yet the old long-delay side won about 70 % of responses.
The history of waiting, not just the amount of food, drove the choice.
How this fits with other research
Blue et al. (1971) showed that big, sudden jumps in delay hurt matching. Fahmie et al. (2013) go further: even after the delay is removed, its shadow lingers.
Okouchi et al. (2006) found that past reinforcement rate alone can speed or slow later responding. The new study adds changeover delay to the list of silent history variables.
Together the papers say the same thing in different ways: past schedules leak into today’s data. Check history before you blame the current contingency.
Why it matters
If you run concurrent schedules in practice or in research, note the delay history of each option. A key that once had a long COD may look “preferred” even after you equalize pay. Fade delays slowly and keep baseline history the same across alternatives. Track choice for several sessions after any schedule tweak to let old contingencies wash out.
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02At a glance
03Original abstract
The present study assessed whether a pattern of responding that develops when choosing between two alternatives generalizes to novel choice tests when alternatives are presented in new combinations. Pigeons were trained on a two-component multiple schedule. In both components, a concurrent variable-interval (VI) 40-s VI 80-s schedule was used. The COD was 1 s in one component and 10 s in the other. The long COD produced consistently longer dwell times than the short COD did. Following training, subjects were presented with four types of probe-test components in which one alternative was drawn from the component with the short COD and one alternative was drawn from the component with the long COD. When the schedule values of the two alternatives were identical (VI 40 vs. VI 40 and VI 80 vs. VI 80), subjects preferred the alternative trained with the long COD (Ms = .78 and .61, respectively). Additionally, subjects preferred the VI 40-s alternative trained with the long COD to the VI 80-s alternative that was trained with the short COD (M = .85). Systematic preference was not observed when subjects were given a choice between the VI 40-s alternative that was trained with the short COD and the VI 80-s alternative that was trained with the long COD. These results demonstrate that a stimulus associated with a longer COD, and thus longer dwell times in baseline training, may be more preferred during probe tests than expected on the basis of the rate of primary reinforcement associated with that stimulus.
Journal of the experimental analysis of behavior, 2013 · doi:10.1002/jeab.44