Neuman, P., Ahearn, W. H., & Hineline, P. N. (1997).
Pigeons' choices between fixed-ratio and geometrically escalating schedules.
Journal of the Experimental Analysis of Behavior,
68, 357-374.
When pigeons choose between situations that provide access to
food reinforcers after a delay, choice is better predicted by
computations based upon sums-of-reciprocals distances from the
point of choice to each of the next three or four reinforcers in
series than by computations of optimality based upon mean rates
of reinforcement. The present experiments were designed to
examine the generality of this finding. Pigeons were exposed to
concurrent-chains schedules in which one brief initial link led
to a fixed-ratio schedule (either 15, 30, or 60, depending on the
condition), and the other link led to a geometrically increasing
progressive-ratio schedule whose rate of escalation was
systematically varied across conditions. Each combination of
fixed-ratio size and escalation rate of the progressive schedule
was assessed at two different levels of deprivation (75% and 80%
of free-feeding weights). Computations based upon the
sums-of-reciprocals principle, treating ratio schedule sizes as
proportional to delays, predicted and described the pigeons'
median switch points better than those based on arithmetic means.
Neither the distance to the next reinforcer (as implied by some
molecular analyses) nor molar optimization (as described by
arithmetic means) were as successful at accounting for patterns
of choice in these situations. Hence, it appears that the birds'
choices were most influenced by the relative proximity of a
choice to several reinforcers in a series of reinforcers, with
each of the less proximal reinforcers having relatively less
influence over the current choice.
Key words: choice patterns, concurrent-chains schedules,
averaging techniques, key peck, pigeons