Laties, V. G., Weiss, B., Clark, R. L., & Reynolds, M. D. (1965).
Overt "mediating" behavior during temporally spaced responding.
Journal of the Experimental Analysis of Behavior,
8, 107-116.
A rat was trained on a schedule that programmed reinforcements
only when a minimum waiting time between successive responses was
exceeded (DRL schedule). It was observed to fill much of the
pause between lever presses with a stereotyped behavioral chain:
it would take its tail in its mouth and nibble it. This behavior
was shown to be functionally related to the efficiency with which
the subject spaced its responses. It is thought to have served as
mediating behavior, providing discriminative stimuli for
appropriate lever presses.
A movie illustrating this rat's performance was made by the authors. You
can view a
brief selection
(1,209K) of the movie in Quicktime format. (See JEAB's Video Page for more information.)
The rat presses the lever and, having waited to do so more than the required
22 seconds after its prior response, produces 6 seconds access to sweetened
condensed milk.
After consuming the milk (during which time the clock does not run), it moves
to the rear of the chamber and starts nibbling on its tail. It does this for
about 10 seconds, drops its tail, moves forward, and again presses the lever.