In the experiment, reported in the Journal of Experimental Psychology 47, 265 - 270 (1954), ten hooded rats deprived of food for 22 hours were released into a straight runway to touch a projecting bar that released food. Successful response was measured as the number of rats that touched the bar within a preset time (either 1.7 s or 2.5 s). After the first 50 trials the rats were divided into fast and slow performers by taking the average of the five fastest and five slowest responses. The figure shows the results for 80 trials grouped into sets of 10 trials.
Experiments of this type invariably show an initial slow response followed by a phase of rapid learning success that rises to near-perfection, followed by a slower approach of perfect knowledge. In contrast, early mathematical models of brain activity tended to produce exponential learning improvement (ie curves with the most rapid learning success at the beginning).
Spence, K. W. (1956) Behaviour Theory and Conditioning. Yale University Press, New Haven.