An index of automatization ability was constructed by assuming that ( I ) the response rate to repeated common stimuli reflects, in part, the ability to benefit from past practice and ( 2 ) such response rates should be corrected for general abiliry level. The relat~onship of such an index to mastery of a novel task was examined. Fifty male Ss were first given distributed and then massed practice trials on a coded additions cask. A second sample of 30 Ss was given twice the number of distributed practice trials followed by massed practice. In both samples, the automatization index related to performances under massed bur not distributed practice. The results were discussed in the context of physiological differences previously found related to the automatization index.Automatized behaviors are behaviors which have been so well practiced and overlearned that a minimum of conscious effort is required for their successful, efficient execution. Such behaviors include the bulk of everyday activities, e.g., maintaining one's balance, walking, writing, reading, talking, maintaining perceptual constancies, etc.The phenomenon of automatization was reported by the introspectionists who while studying attention processes noticed that the act of performing a task tended to fade from consciousness as learning accrued with practice (Ach, 1905).The amounts of physical and mental effort as well as the amount of time required to perform tasks were also noted to diminish as non-essential parts of the task performance disappeared with practice (Solomons, 1899; Thorndike, 1898). The tendency of practice to induce behavioral parsimony has been variously termed the "law of least effort," or "least action" and the "principle of maxima and minima" ( Adams, 1931 ) .The inuospectioniscs also noted that as a task became automatized it interferred less with the simultaneous performance of other tasks (James, 1909;Solomons, 1899). Ford ( 1929) interpreted this phenomenon with the teleological proposition that the function of learning is to reduce the amount of attention required for the performance of a given task in order to make more attentional energies available for the acquisition of new tasks or behaviors.