1. (Science: neurology) An increase of force or strength; denoting specifically the increased sharpness of the patellar reflex when the patient at the same time closes the fist tightly or pulls against the flexed fingers or contracts some other set of muscles.
See: jendrassik's manoeuvre.
3. (Science: psychology) In conditioning, the totality of the process in which the conditioned stimulus is followed by presentation of the unconditioned stimulus which, itself, elicits the response to be conditioned.