Choice in a variable environment: Every reinforcer counts

Six pigeons were trained in sessions composed of seven components, each arr anged with a different concurrent-schedule reinforcer ratio. These componen ts occurred in an irregular order with equal frequency, separated by 10-s b lackouts. No signals differentiated the different reinforcer ratios. Condit ions 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 m inute. 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 b oth 4 and 12 reinforcers per component. Within components, log response-all ocation ratios adjusted rapidly as more reinforcers were delivered in the c omponent, and the slope of the choice relation (sensitivity) leveled off at moderately high levels after only about eight reinforcers. When the carryo ver from previous components was taken into account, the number of reinforc ers in the components appeared to have no systematic effect on the speed at which behavior changed after a component started. Consequently, sensitivit y values at each reinforcer delivery were superimposable. However, adjustme nt 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 smalle r effect than the one before, but single reinforcers from the other alterna tive ("disconfirming") always had a large effect. Choice in the prior compo nent carried over into the next component, and its effects could he discern ed even after five or six reinforcers into the next component. A local mode l of performance change as a function of both reinforcement and nonreinforc ement is suggested.