Krägeloh, C.U., Elliffe, D.M., & Davison, M. (2006).
Contingency discriminability and peak shift in concurrent schedules.
Journal of the Experimental Analysis of Behavior, 86, 11-30.
We investigated the effects of discriminative stimuli on choice in a highly variable
environment using a procedure in which multiple two-key concurrent VI VI components
changed every 10 reinforcers and were signaled by differential flashes of red and
yellow keylights. Across conditions, five pigeons were exposed to a number of
different combinations of the following component reinforcer ratios:
27:1, 9:1, 3:1, 1:1, 1:3, 1:9, 1:27. Overall, there was clear control by
the component signals in that preference, early in components and particularly
before any reinforcers had been delivered, was ordinally related to the signaled
reinforcer ratios. In conditions in which only two components arranged unequal
reinforcer ratios (e.g., 27:1 and 1:27) with the remaining components arranging
1:1 reinforcer ratios, preference before the first reinforcer in a component
showed peak shift in that the most extreme preference did not occur in the unequal
reinforcer-ratio components, but in 1:1 components further towards
the ends of the stimulus dimension. The
contingency-discriminability model (Davison & Nevin, 1999) was fitted to
the data and provided an excellent description of the interactions between
stimulus and reinforcer effects in a highly variable environment.
Key words: choice, stimulus control, contingency discriminability, peak shift,
multiple-concurrent schedules, key peck, pigeons