Primarily a feasibility study, the research reported is based on Eysenck's hypothesis that conditionability is a unitary factor related to introversion-extroversion and attention span. Thirty infants, representing a random sampling of race, sex, and socioeconomic background, were tested on three consecutive days at ages 3 months, 5 months, 9 months, and 12 months. Tests based on existing methods of successful infant conditioning were adapted to infants' abilities at each age, but at each test time included eye blink, vocalization, head turn, discrimination and single-stimulus conditioning. Tests of attention-span and the Bayley Test of Mental and Motor Development were also given each time. The subjects will be tested again at age 3 and at age 7, using standard IQ and personality tests. The feasibility of this longitudinal study was established, and conclusions were drawn about the usefulness of the various conditioning procedures employed. Further research leading to standardized procedures and a test of conditionability is needed, to give clues to the child's individual learning style. Figures showing the apparatus for the tests used in this study are included. (Author/NH)