Actions influence sensory processing in a complex way to shape behavior. For example, it has been hypothesized that during actions, a copy of motor signals-termed corollary discharge or efference copy-can be transmitted to sensory regions and modulate perception. Such motor-to-sensory transformation has been evident among animal species and is extended to human speech production and control. The inhibitory function of the motor copies has been supported by the suppression of sensory responses during action execution. However, the sole inhibitory function is challenged by mixed empirical observations as well as multifaceted computational demands for behaviors. Theories have been proposed that corollary discharge and efference copy may be two separate functional forms that are generated at different stages of intention, preparation, and execution during actions. We tested these theories using speech in which we can precisely control and quantify the course of action. Specifically, we hypothesized that the content in the motor signals available at distinct stages of speech preparation determined the nature of signals (corollary discharge vs. efference copy) and constrained their modulatory functions on auditory processing. In three electroencephalography (EEG) experiments using a novel delayed articulation paradigm, we found that preparation without linguistic contents suppressed auditory responses to all speech sounds, whereas preparing to speak a syllable selectively enhanced the auditory responses to the prepared syllable. A computational model demonstrated that a bifurcation of motor signals could be a potential algorithm and neural implementation to achieve the distinct functions in the motor-to-sensory transformation. These consistent results suggest that distinct motor signals are generated in the motor-to-sensory transformation and integrated with sensory input to modulate perception.