Baum, W. M., Schwendiman, J. W., & Bell, K. E. (1999).
Choice, contingency discrimination, and foraging theory.
Journal of the Experimental Analysis of Behavior,
71, 355-373.
Four pigeons were trained on eight or nine pairs of independent
concurrent variable-interval schedules. The range of
reinforcement ratios included extreme ratios (up to 532 to 1).
Large samples of stable performance were gathered. Contrary to
the findings of Davison and Jones (1995), the generalized
matching law described choice more accurately than a
contingency-discriminability model. Taking small samples (5 to 10 sessions)
and applying a more liberal stability criterion used by Davison
and Jones only increased the unsystematic variance in the data
and in estimates of generalized-matching-law sensitivity. Because
changing to dependent scheduling and inserting a changeover delay
had no systematic effect, the deviations from generalized
matching reported by Davison and Jones probably arose from
imperfectly discriminated stimuli. Analysis of visits revealed
that visits to the nonpreferred alternative were brief and
approximately constant. When choice between the preferred (rich)
and nonpreferred (lean) alternatives, regardless of position, was
analyzed according to the generalized matching law, sensitivities
approximated 1.0, with bias in favor of the lean alternative.
This bias, which arose from an excessive frequency of visits to
the lean alternative, explains undermatching as the result of
fitting one line to a choice relation that consists of two
displaced lines, both with a slope of 1.0. The pattern of
deviation from the generalized matching line confirmed this
account. The findings suggest an alternative analysis of choice
that focuses on probability of visiting the lean alternative as
the dependent variable. This probability was directly
proportional to ratio of reinforcement. Matching,
undermatching, and overmatching may all be explained by a view of
concurrent performance based on foraging theory, in which
responding occurs primarily at the rich alternative and is
occasionally interrupted by brief visits to the lean alternative.
Key words: choice, generalized matching law,
contingency-discriminability model, foraging theory, visit
duration, key peck, pigeons