The ability to sense and use the body parts in an organized and differentiated manner is a precursor of body knowledge in infancy. To acquire this ability, the infant's brain might explore the perceptual consequences of its bodily actions. Undifferentiated body movements would gradually be replaced by more precise actions. Only a very few studies have tested this ‘global-to-local’ hypothesis, and none of them have so far been replicated. In this study, we assessed arm differentiation in 4-, 6-, and 8-month-old infants using a new contingency detection task in which infants have to detect a contingency between one of their arms’ activity and an audiovisual stimulus on a screen. We found that 4- to 8-month-old infants seem to be able to use their arms in a differentiated manner. However, surprisingly, we were not able to show a developmental trend in arm differentiation between 4 and 8 months of age.