McDevitt, M. A., & Williams, B. A. (2001).
Effects of signaled versus unsignaled delay of reinforcement on choice.
Journal of the Experimental Analysis of Behavior,
75, 165-182.
Pigeons chose between 5-s and 15-s delay-of-reinforcement
alternatives. The first key peck to satisfy the choice schedule
began a delay timer, and food was delivered at the end of the
interval. Key pecks during the delay interval were measured, but
had no scheduled effect. In Experiment 1, signal conditions and
choice schedules were varied across conditions. During unsignaled
conditions, no stimulus change signaled the beginning of a delay
interval. During differential and nondifferential signal
conditions, offset of the choice stimuli and onset of a delay
stimulus signaled the beginning of a delay interval. During
differential signal conditions, different stimuli were correlated
with the 5-s and 15-s delays, whereas the same stimulus appeared
during both delay durations during nondifferential signal
conditions. Pigeons showed similar, extreme levels of preference
for the 5-s delay alternative during unsignaled and
differentially signaled conditions. Preference levels were
reliably lower with nondifferential signals. Experiment 2
assessed preference with two pairs of unsignaled delays in which
the ratio of delays was held constant but the absolute duration
was increased fourfold. No effect of absolute duration was found.
The results highlight the importance of delayed primary
reinforcement effects and challenge models of choice that focus
solely on conditioned reinforcement.
Key words: delay of reinforcement, unsignaled delay,
differentially signaled delay, nondifferentially signaled delay,
choice, key peck, pigeons