A visuospatial reaction time task was used to gain an online measure of learning as subjects responded manually to strings of stimuli containing embedded transitional probabilities. We hypothesized that items within a stimulus sequence that have low transitional probabilities will be learned more slowly than items that have high transitional probabilities. Subjects were instructed to make button press responses to stimulus strings composed of sequences of lights. Items in the strings were organized into triplets, with a low average transitional probability for the first item in a triplet, and transitional probabilities of 1.0 for the second and third items. Results indicate that learning is poorer for stimulus items with low transitional probabilities than for stimulus items with high transitional probabilities. This work ties together a number of previous investigations of sequence learning, and has implications for how more complicated, hierarchically structured sequential input, such as language, may be learned.