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Zarcone, T.J., Chen, R. & Fowler, S.C. (2009). Effects of differing response-force requirements on food-maintained responding in C57BL/6J mice. Journal of the Experimental Analysis of Behavior. 92, 257–274.
In the results section, Figure 4, (pg. 263) and the description of response rates incorrectly described data from BALB/cJ mice.
The correct figure and description for the C57BL/6J strain are printed below.
Figure 4 shows responses per minute during the last 5 days of the 2-g training phase. Response rates at the 2-g requirement averaged at 4 responses per minute until the last session when response rates increased above 10 responses per minute. Data from the first exposure to the 4-g requirement were lost to equipment failure. By the second session, however, all response rates averaged 10 per minute. Of the remaining four sessions, responses were relatively stable. During the first exposure, shifting to the 8-g requirement resulted in an increase in disk pressing. The shift to the 16-g requirement also resulted in an increase in disk-press rate in the first session. Continued exposure to the 16-g requirement decreased disk pressing back to around 10 per minute. Changing to the 32-g requirement increased the between-subject variability in disk-press rate (see error bars), and response rate. Continued exposure to the 32-g requirement decreased disk pressing back to around 10 per minute.
During the second exposure to the 2-g requirement (Figure 4 bottom panel), disk-press rate was more stable than in the first exposure. Shifting to the second 4-g requirement did not change response rates. After shifting to the 8-g requirement, response rates slightly increased again. The shift to the 16-g requirement increased the response rates, which remained higher, but were more variable (see error bars). Response rates during the second exposure to the 32-g requirement were not as variable as those of the first exposure, but did show the initial increase in rate with a steady decrease back to around 11 per minute.
For the 2-g force requirement, all the criterion responses are the same (only open circles). Any direct comparison between criterion responses across different force requirements is confounded by changing the definition of the operant. Criterion response rate can be analyzed across sessions within the same force requirement. For the most part, criterion response rates remained stable across sessions within a force requirement. Only the 8-g requirement and the first 32-g exposure show a slight increase in response rate across sessions for this strain.