Davison, M., & Baum, W. M. (2000).
Choice in a variable environment: Every reinforcer counts.
Journal of the Experimental Analysis of Behavior,
74, 1-24.
Six pigeons were trained in sessions composed of seven
components, each arranged with a different concurrent-schedule
reinforcer ratio. These components occurred in an irregular order
with equal frequency, separated by 10-s blackouts. No signals
differentiated the different reinforcer ratios. Conditions lasted
50 sessions, and data were collected from the last 35 sessions.
In Part 1, the arranged overall reinforcer rate was 2.22
reinforcers per minute. Over conditions, number of reinforcers
per component was varied from 4 to 12. In Part 2, the overall
reinforcer rate was six per minute, with both 4 and 12
reinforcers per component. Within components, log
response-allocation ratios adjusted rapidly as more reinforcers
were delivered in the component, and the slope of the choice
relation (sensitivity) leveled off at moderately high levels
after only about eight reinforcers. When the carryover from
previous components was taken into account, the number of
reinforcers in the components appeared to have no systematic
effect on the speed at which behavior changed after a component
started. Consequently, sensitivity values at each reinforcer
delivery were superimposable. However, adjustment to changing
reinforcer ratios was faster, and reached greater sensitivity
values, when overall reinforcer rate was higher. Within a
component, each successive reinforcer from the same alternative
("confirming") had a smaller effect than the one
before, but single reinforcers from the other alternative
("disconfirming") always had a large effect. Choice in
the prior component carried over into the next component, and its
effects could be discerned even after five or six reinforcers
into the next component. A local model of performance change as a
function of both reinforcement and nonreinforcement is suggested.
Key words: concurrent schedules, environmental variability,
choice, generalized matching, contingency discriminability, key
peck, pigeons