Effects of differing response-force requirements on food-maintained responding in C57Bl/6J mice.
Making a response physically harder increases total output, it does not punish the behavior.
01Research in Context
What this study did
The team asked mice to press a tiny metal tab for food. Each press had to be harder than the last one. The force started at 4 grams and climbed to 32 grams across sessions.
They used C57Bl/6J mice, a common lab strain. The schedule was variable-interval, meaning food could drop at any moment. They counted total presses and looked for signs of punishment.
What they found
When the force jumped, pressing paused for a few minutes. Then the mice went back to work. Total presses actually rose, not fell, at every level except the top 32 g.
The mice never stopped completely. The authors say this kills the idea that high force equals punishment. Instead, the animals just worked harder to keep the food coming.
How this fits with other research
Grace (1995) wrote that making a response harder usually cuts behavior. The mouse data look opposite at first glance. The gap is real: Grace (1995) summed human-applied effort studies, while the mice faced pure physics. The lesson is that "effort" in the chair and "force grams on a lever" are not the same variable.
Pinkston et al. (2018) later asked if force matters during extinction. They found zero effect: only past reinforcement rate predicted how long pigeons kept pecking. Together, the two papers show force tweaks momentary effort, not long-term staying power.
Older shock studies like Hake et al. (1967) showed graded punishment with electric shock. High lever force did not copy that curve, again showing force is a poor punisher.
Why it matters
If you think adding physical work will cut problem behavior, think twice. The mouse data say the client may just push harder and emit more responses overall. Save high-force requirements for exercise or endurance goals, not for suppression. When you do use them, watch for fatigue in smaller clients, just as the petite C57Bl/6J mice failed at 32 g.
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02At a glance
03Original abstract
The effect of force requirements on response effort was examined using inbred C57BL/6J mice trained to press a disk with their snout. Lateral peak forces greater than 2 g were defined as responses (i.e., all responses above the measurement threshold). Different, higher force requirements were used to define criterion responses (a subclass of all responses) that exceeded the requirement and produced a reinforcer. The reinforcer was sweetened, condensed milk, 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 initially decreased criterion response rates, but criterion response rates recovered with continued exposure, except at the 32-g requirement. Response rates for all measured responses initially increased with increasing force requirements, but then decreased with continued exposure. The second exposure series produced more stable response rate changes than the first series. 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. The C57BL/6J inbred strain generated average force output similar to CD-1 outbred stock mice trained on the same force requirements. C57BL/6J inbred strain mice differed from CD-1 mice in initial response rates (for all responses above threshold) and had lower response rates at the 16 and 32 g requirements resulting in lower total force output. These data show for both mice types that increased force requirements resulted in increased overall responding (all measured responses), which contradicts a punishment interpretation of criterion response decrements. C57BL\6 inbred mice showed individual differences comparable to the outbred CD-1 stock. C57BL/6 mice did not maintain responding as well at the higher force requirements, which may be due to their small body size and weight, compared to the larger and heavier CD-1 mice.
Journal of the experimental analysis of behavior, 2009 · doi:10.1901/jeab.2009.92-257