When unintended movements “leak” out: A startling acoustic stimulus can elicit a prepared response during motor imagery and action observation

► Subjects performed imagery, observation and physical practice of a keylift RT task. ► Selected trials replaced “go” signal with startling acoustic stimulus (SAS-124 dB). ► Partial unimanual responses were triggered by the SAS during imagery and observation. ► Results are attributed to low level neural activation that is increased by the SAS. ► Results provide a novel delineation of preparatory processes during covert actions.