During lexical access, listeners use both signal-based and knowledge-based cues, and information from the linguistic context can affect the perception of acoustic speech information. Recent findings suggest that the various cues used in lexical access are implemented with flexibility and may be affected by information from the larger speech context. We conducted 2 experiments to examine effects of a signal-based cue (distal speech rate) and a knowledge-based cue (linguistic structure) on lexical perception. In Experiment 1, we manipulated distal speech rate in utterances where an acoustically ambiguous critical word was either obligatory for the utterance to be syntactically well formed (e.g., Conner knew that bread and butter (are) both in the pantry) or optional (e.g., Don must see the harbor (or) boats). In Experiment 2, we examined identical target utterances as in Experiment 1 but changed the distribution of linguistic structures in the fillers. The results of the 2 experiments demonstrate that speech rate and linguistic knowledge about critical word obligatoriness can both influence speech perception. In addition, it is possible to alter the strength of a signal-based cue by changing information in the speech environment. These results provide support for models of word segmentation that include flexible weighting of signal-based and knowledge-based cues.