Preserved nodal number effects under equal reinforcement

The present set of experiments tested the hypothesis
that the nodal number effects observed in previous studies of
stimulus equivalence were due to the confounding factor of
training structure that resulted in unequal reinforcement across
trial types. In Experiment 1, two 5-member equivalence
classes were trained across equal and unequal reinforcement
conditions, both with and without a limited hold. A
significant nodal effect, as measured by response speed, was
found in the equal reinforcement, no-limited-hold condition.
In Experiment 2, two 6-member equivalence classes were
trained in equal and unequal reinforcement conditions
without limited hold. In a transfer-of-function test, clear
nodal effects were observed in the equal reinforcement
condition. Experiment 3 replicated and extended the findings
of Experiments 1 and 2 with an increased number of baseline
training trials. The results of the present study suggest that the
effects of nodal number are independent of differential
reinforcement. Furthermore, a transfer-of-function test was
most sensitive to nodal effects, response speed was the next
most sensitive measure, and response accuracy was the least
sensitive measure of nodal effects.