Studies of the infant's distribution of attention to stimuli of varying complexity, and of his differential attention to familiar versus novel stimuli (discrepancy), have attempted to shed light on the development of cognitive structures in the non-verbal infant. The subjects have typically been normal infants ages 4 to 6 months. For testing, the infant is placed in an infant seat on a table in a small room, with the mother seated to the side and rear of him. Visual or auditory stimuli are presented to the infant and his response behavior is recorded. Two dependent variables measured have been first fixation (the length of the infant's first visual fixation to the stimulus during any single presentation), and cardiac deceleration (the degree to which the infant's heart rate slows during a fixation). Past studies are cited regarding their differing emphases on particular aspects of attention and their findings on individual differences. Typically, the infant habituates (responds less) to repeated presentations of stimuli. Work in this area is just beginning, but study results thus far indicate that habituation and response to discrepancy may be important indices of cognitive functioning. (NH)