In previous research of tonal phonology, contour tones were assumed to be phonologically presented not only as a sequence of level tones but also as a single unit. Obligatory Contour Principle (OCP) constraints, by extension, were thought to prohibit identical level tones associated to adjacent terminal nodes (OCP-Terminal) and identical adjacent tonal units (OCP-Unit). This proposal has nevertheless been challenged theoretically and empirically. This study seeks to offer new experimental evidence to help solve the debate by comparing the learnability of the two OCP generalizations in an artificial grammar learning paradigm. In Exp I, we exposed disyllabic tonal patterns conforming either to OCP-Terminal or to OCP-Unit to two target groups of learners, who were then tested if they could extend the hidden generalization to their auditory acceptability judgment of novel disyllabic items. Exp II had the same exposure phase but required learners to produce novel disyllabic items with tonal combinations of their choice. In both experiments, the two target groups demonstrated signs of learning target OCP generalizations from different channels. Crucially, learners implicitly acquired the OCP-Terminal generalization but only learned the OCP-Unit pattern as explicit knowledge. These findings led us to conclude that OCP-Unit may not be involved in implicit and automatized phonological computation.