The author describes the central role of contingency detection in early socioemotional development. It has been proposed (Gergely & Watson, 1999) that infants are innately equipped with a complex perceptual mechanism, the "contingency detection module," which functions to establish the primary representation of the bodily self as well as the later orientation toward reactive social objects. According to the "contingency switch" model, the target value of the module that is initially genetically set to preferentially explore perfectly response-contingent stimulation is "switched" at around 3 months toward a preference for less-than-perfect social contingencies. It is hypothesized that the primary cause of childhood autism is a genetic defect, due to which the normal process of switching contingency preference at around 3 months does not take place. Preliminary results from an experimental study to test this model are reported. The study contrasts the preferential reactions of normal children and children with autism to perfect versus imitative (high-but-imperfect) contingencies. The results provide support for the contingency switch hypothesis of the etiology of childhood autism.