Hackenberg, T. D., & Joker, V. R. (1994).
Instructional versus schedule control of humans' choices in situations of diminishing returns.
Journal of the Experimental Analysis of Behavior,
62, 367-383.
Four adult humans chose repeatedly between a fixed-time schedule
(of points later exchangeable for money) and a progressive-time
schedule that began at 0 s and increased by a fixed number of
seconds with each point delivered by that schedule. Each point
delivered by the fixed-time schedule reset the requirements of
the progressive-time schedule to its minimum value. Subjects were
provided with instructions that specified a particular sequence
of choices. Under the initial conditions, the instructions
accurately specified the optimal choice sequence. Thus, control
by instructions and optimal control by the programmed
contingencies both supported the same performance. To distinguish
the effects of instructions from schedule sensitivity, the
correspondence between the instructed and optimal choice patterns
was gradually altered across conditions by varying the step size
of the progressive-time schedule while maintaining the same
instructions. Step size was manipulated, typically in 1-s units,
first in an ascending and then in a descending sequence of
conditions. Instructions quickly established control in all 4
subjects but, by narrowing the range of choice patterns, they
reduced subsequent sensitivity to schedule changes. Instructional
control was maintained across the ascending sequence of
progressive-time values for each subject, but eventually
diminished, giving way to more schedule-appropriate patterns. The
transition from instruction-appropriate to schedule-appropriate
behavior was characterized by an increase in the variability of
choice patterns and local increases in point density. On the
descending sequence of progressive-time values, behavior appeared
to be schedule sensitive, sometimes even optimally sensitive, but
it did not always change systematically with the contingencies,
suggesting the involvement of other factors.
Key words: instructional control, schedule control, verbal
behavior, choice, progressive-time schedules, fixed-time
schedules, key press, adult humans