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. Author manuscript; available in PMC: 2010 Mar 17.
Published in final edited form as: Behav Brain Res. 2008 Nov 27;198(2):298–305. doi: 10.1016/j.bbr.2008.11.033

Figure 1.

Figure 1

Theoretical response rate functions for ratio schedules specified by MPR (Equation 1). Left Panel: The descending limb intercepts the x-axis at a (signaled by arrows), thus providing a measure comparable to the breakpoint in a progressive-ratio procedure. Middle Panel: Extrapolation to the left (dotted lines) intercepts the y-axis at the maximum response rate, 1/δ. Right Panel: The increase in rate over small to moderate ratios is due to the increasing saturation of memory with the target response, with the rate of saturation given by λ; the mean capacity is 1/λ seconds of responding. If the rate is fast, perhaps because of a small memory capacity or complicated response, the function will quickly rise into the decreasing asymptote of the right limb. Larger capacities, associated with smaller values of λ, will rise more slowly.