Effects of differing response-force requirements on food-maintained responding in CD-1 mice.
High effort doesn’t punish behavior; it just spreads tries between strong and weak responses.
01Research in Context
What this study did
Scientists watched mice press a lever for food.
They made the lever harder to push in small steps.
A computer counted every push, even the weak ones that did not trip the switch.
What they found
Harder levers cut the number of full-strength presses.
But the mice still pressed; many tries were just too light to count in old studies.
Total presses stayed high, so food still worked as a reward.
How this fits with other research
Older rat studies like Anonymous (1995) and Lowe et al. (1995) said high force lowers rate.
Those papers only counted strong presses, so they missed the light ones.
Pinkston et al. (2017) later saw the same thing with human voices: count every response and the drop disappears.
Llewellyn et al. (1976) already hinted at this on variable-interval schedules, but the mouse study nailed the point.
Why it matters
When a client slows down, check if the response got harder.
Maybe they are still trying, just not hard enough for your sensor.
Lower the force target or widen the count window before you call the task aversive.
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02At a glance
03Original abstract
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.
Journal of the experimental analysis of behavior, 2007 · doi:10.1901/jeab.2007.88-381