Reid, A. K., Chadwick, C. Z., Dunham, M., & Miller, A. (2001).
The development of functional response units: The role of demarcating stimuli.
Journal of the Experimental Analysis of Behavior,
76, 303-320.
An experiment with rats examined the roles of demarcating stimuli
and differential reinforcement probability on the development of
functional response units. It examined the development of units
in a probabilistic, free-operant situation in which the presence
of demarcating stimuli was manipulated. In all conditions,
behavior became organized into two-response sequences framed by
changes in local reinforcement probability. A tone demarcating
the beginning and end of contingent response sequences
facilitated the development of functional response units, as in
chunking, but the same units developed slowly in the absence of
the tone. Complex functional response units developed even though
reinforcement contingencies remained constant. These findings
demonstrate that models of operant learning must include a
mechanism for changing the response unit as a function of
reinforcement history. Markov models may seem to be a natural
technique for modeling response sequences because of their
ability to predict individual responses as a function of
reinforcement history; however, no class of Markov chain can
incorporate changing response units in their predictions.
Key words: response acquisition,
behavioral unit, response sequences, behavioral variability,
response stereotypy, chunking, rats