(1) In the testing of hearing, the abnormally greater increase in loudness in response to increments in intensity of the acoustic stimulus in an ear with a sensory hearing loss compared with that of a normal ear. (2) In neurophysiology, the activation of additional neurons (spatial recruitment) or an increase in their firing rate (temporal recruitment). SYN: recruiting response.irradiation (3). (3) The adding of parallel channels of flow in any system. [Fr. recrutement, fr. L. re-cresco, pp. -cretus, to grow again]