Pioneering research has shown that infants are capable of perceptual discrimination and has provided some indication of the nature of the discrimination; that is, what stimuli are differentiable. Studies have demonstrated that significant effects exist, in stimulus-pair comparisons, for age of infant, speed of movement of stimulus during perception, and for the age-speed interaction. The stimulus involved was checkerboard designs. It has been discovered that the looking pattern of infants varies with age. The younger infant takes fewer but longer looks, while the older infant takes more but shorter looks. It has also been found that younger infants are more likely, when finally shifting their gaze, to shift it back to the first stimulus. This factor cuts into the reliability of using pair-comparisons for measuring infant stimulus preference, especially because trial times are often brief (about 30 seconds). It is possible to measure preference by just presenting one stimulus and recording fixation time. It was discovered that 10-week-old children looked at the most complex of three checkerboard stimuli the most and the least complex stimulus the least. This was also found true of 20-week-old children. Eight-week-old children preferred the medium complexity stimulus. A hypothesis now under investigation is that younger than 8-week-old children will look at the least complex stimulus the most. (WD)