Zarcone, T.J., Chen, R. & Fowler, S.C.(2007).
Effects of differing response-force requirements on food-maintained responding in CD-1 mice.
Journal of the Experimental Analysis of Behavior, 88, 381-393.
The effect of force requirements on response effort was examined using outbred (CD-1) mice trained to press a
disk with their snout. Lateral peak forces greater than 2 g were defined as threshold responses (i.e., all
measured responses). Different force requirements were used to define criterion responses (a subclass of
threshold responses) that exceeded the requirement. The reinforcer was sweetened, condensed milk, and it was
delivered upon response termination. All mice were exposed to two ascending series of criterion force
requirements (2, 4, 8, 16, and 32 g). Increasing the force requirement decreased criterion response rates, but
increased threshold response rates. The time-integral of force (area under the force-time curve for individual
responses, which is proportional to energy expenditure for each response) increased with the increase in the
force requirement. These results conflict with the hypothesis that higher force requirements have aversive
qualities and suggest that increased force requirements are more analogous to intermittent schedules of
reinforcement. These data suggest that estimations of effort or energy expenditure should be measured
independently of the force requirement. Individual differences in responding were found for the CD-1 outbred
stock.
Key words: operant, effort, force, disk press, CD-1 mice