The repetition or continuation of experimental conditions and/or stimuli after given responses or after their absence (especially, in a discrete-trial simultaneous discrimination, after errors). For example, stimuli on one trial may be repeated on the next if an error occurred or if, in a trial of limited duration, no response occurred. In a free-operant case, a multiple VI extinction schedule may be arranged so that each response during the extinction component delays the onset of the VI component. The term can refer to any procedure that arranges continued or repeated opportunities for responses in alternative classes until a given response does (or does not) occur. Its colloquial origins imply procedures that eventually force an organism to emit a correct response , but the technical usage does not exclude procedures in which the alternative response classes cannot easily be categorised as correct responses and errors.