Infant sex differences in operant fixation with visual and auditory reinforcement

Forty-eight 14-week-old infants were reinforced for fixation of either a left or right circle with an auditory or visual stimulus. Each subject was tested for a baseline period, and three conditioning-extinction phases, during which three intensities were presented in one of three orders. Subjects performed significantly better during the final two conditioning periods than during baseline or the first conditioning period. There was a significant interaction between sex, intensity and modality during the first conditioning period, indicating that males performed better than females with the visual stimulus across intensities, while females performed better than males with low intensity auditory stimuli.