Negations, i.e., instructions on what not to do, come with severe challenges for our cognitive system. These include ironic effects, evident in people doing exactly what they are told not to do, increased errors, and significant response time costs for successfully enacted negations when compared to affirmative instructions.
Here, we tested how the cognitive system enacts instructions that include multiple negations, meaning several bits of information have to be negated to select one correct response. We find that negation costs add up, evident by increasing negation costs for increasing negation demands. This suggests that every negation is processed on its own, and additional negations cannot benefit from already ongoing negation processing. Thereby, the processing of negations presents a structural limitation in action control.