Despite an extensive history of study, the effects of phonetic context are only known to affect small units of speech (e.g., formant transitions, function words). Critical aspects of speech perception, however, occur at larger scales. The series of experiments reported here investigated the effects of contextual speech rate on perception of a large unit of speech, namely sentences. In particular, there was an effect of relative rate on sentence comprehension – the rate of a sentence compared to the average rate of all other sentences within the same conversation-length period of speech – such that relatively slow sentences were better comprehended than relatively fast sentences (Experiment 1); however, differences in perceptual learning between the relatively slow and the relatively fast rates accounted for the effect of relative rate (Experiment 2). The results of these studies, therefore, do not support an effect of contextual speech rate on sentence comprehension. Finally, based on the results of a modified version of Experiment 1 in which context sentences were replaced with non-speech sounds (i.e., 1-channel noise vocoded speech), exposure to temporal information was not sufficient for generalization of perceptual learning (Experiment 3). These experiments are a novel investigation into both the effects of phonetic context on sentence comprehension, and the efficacy of non-speech sounds on generalization of perceptual learning.