The Effects Of Speech Motor Preparation On Auditory Perception
Perception and action are coupled via bidirectional relationships between sensory and motor systems. Motor systems influence sensory areas by imparting a feedforward influence on sensory processing termed â€œmotor efference copyâ€ (MEC). MEC is suggested to occur in humans because speech preparation and production modulate neural measures of auditory cortical activity. However, it is not known if MEC can affect auditory perception. We tested the hypothesis that during speech preparation auditory thresholds will increase relative to a control condition, and that the increase would be most evident for frequencies that match the upcoming vocal response. Participants performed trials in a speech condition that contained a visual cue indicating a vocal response to prepare (one of two frequencies), followed by a go signal to speak. To determine threshold shifts, voice-matched or -mismatched pure tones were presented at one of three time points between the cue and target. The control condition was the same except the visual cues did not specify a response and subjects did not speak. For each participant, we measured f0 thresholds in isolation from the task in order to establish baselines. Results indicated that auditory thresholds were highest during speech preparation, relative to baselines and a non-speech control condition, especially at suprathreshold levels. Thresholds for tones that matched the frequency of planned responses gradually increased over time, but sharply declined for the mismatched tones shortly before targets. Findings support the hypothesis that MEC influences auditory perception by modulating thresholds during speech preparation, with some specificity relative to the planned response. The threshold increase in tasks vs. baseline may reflect attentional demands of the tasks.