Landon, J., & Davison, M. (2001).
Reinforcer-ratio variation and its effects on rate of adaptation.
Journal of the Experimental Analysis of Behavior,
75, 207-234.
Six pigeons were trained in sessions that consisted of six or
seven concurrent-schedule components, each of which could have a
different reinforcer ratio arranged in it. The components were
unsignaled and occurred in a random order separated by 10-s
blackouts. The overall reinforcer rate arranged in each component
was 2.22 reinforcers per minute. In Experiment 1, the range of
reinforcer ratios in the seven components was varied from a
condition in which the ratios were always 1:1, to a condition in
which the ratios varied between concurrent variable-interval 27 s
extinction (EXT) and concurrent extinction variable-interval 27 s
(ratios of 1:EXT, 9:1, 3:1, 1:1, 1:3, 1:9, EXT:1). In Experiment
2, the range of reinforcer ratios was always 27:1 to 1:27, and
the presence and absence of the intermediate reinforcer ratios
used in Experiment 1 (9:1, 3:1, 1:1, 1:3, 1:9) were investigated.
Log response-allocation ratios in components changed rapidly with
increasing numbers of reinforcers in components, and Experiment 1
showed that sensitivity to reinforcement was usually higher when
the range of reinforcer ratios was greater. When the range of
reinforcer ratios was kept constant in Experiment 2, the presence
or absence of less extreme reinforcer ratios had no clear effect
on sensitivity. At a local level, individual reinforcers had
predictable quantitative effects on response ratios: Successive
same-alternative reinforcers in a component had rapidly
diminishing effects in both experiments. Reinforcers obtained on
the opposite alternative to one or more prior reinforcers always
had large effects on preference, and these changes were greater
when the range of reinforcer ratios was greater. The effects of
such reinforcers in changing preference were enhanced, and
produced clear preference reversals, when intermediate reinforcer
ratios were absent in Experiment 2. Two processes, one local to
reinforcers and one with a longer time course, may be necessary
to account for these results.
Key words: concurrent schedules, choice, generalized matching,
behavior change, reinforcer-ratio variation, key peck, pigeons