Bron, A., Sumpter, C. E., Foster, T. M., & Temple, W. (2003).
Contingency discriminability, matching, and bias in the concurrent-schedule
responding of possums (Trichosurus vulpecula).
Journal of the Experimental Analysis of Behavior,
79, 289-306.
Six possums (Trichosurus vulpecula) responded under
dependent concurrent variable-interval variable-interval
schedules of reinforcement. Over 15 conditions, barley–carob
was one reinforcer with the other reinforcer consisting of Coco
Pops;rm, coconut, or a barley–carob mixture with 0%, 2%, 4%,
or 6% salt added to the barley. The schedules were both
variable-interval 40 s. As has been found with other species,
behavior on the concurrent schedules was biased by the type of
feed, with the 6% salt and the coconut giving the greatest biases
towards the barley–carob mixture. The schedules were varied
over 17 conditions using the barley–carob mixture alone or the
barley–carob mixture versus the mixture with 4% or 6% salt.
Both the contingency-discriminability model (Davison &
Jenkins, 1985) and the generalized matching law described the
data from the three sets of conditions equally well. Both gave
similar measures of bias; however, some of the parameter values
found with the contingency discriminability model were
uninterpretable. Thus, any argument for this model based on the
interpretability of the parameter values becomes weak. It is
worth retaining the generalized matching law as a descriptor of
such data.
Key words: concurrent schedules, contingency discriminability, matching,
food preference, bias, lever press, possum