|Weiss and Laties (1961) taught laboratory rats to press a lever for short bursts of radient heat (from an infrared lamp) while the rats were being exposed to a cold environment. The figure to right shows the experimental setup.|
The figure below shows the sub-dermal skin temperature (upper panel) and cumulative lever-presses (lower panel) as functions of time for five rats. Graphs on the left show the first hour of exposure to the cold; those on the right show Hour before and after lever-pressing for heat began. (The bottom panel is the exception as this rat began responding almost immediately.) The cumulative recorder pen reset to bottom every 15 minutes.
A curious feature of this performance is that most of the rats failed to engage in any lever-pressing for several hours after being placed in the cold; instead they hunkered down and shivered. Weiss and Laties suggested that this latter activity may be the rat's innate way to deal with being cold, giving way to lever-pressing only when shivering failed to prevent a further drop in skin temperature.
In another phase of the study, Weiss and Laties varied the wattage to the heat lamp. The figure below shows how the rate of lever-pressing varied as a function of this wattage. In general, as one would predict from control theory, the more heat generated by each operation of the lamp, the lower the rate of lever-pressing and thus of heat-burst "reinforcements."
Weiss, B., & Laties, V. G. (1961). Science, 133, 1338-1344.