THE RECRUITMENT of loudness phenomenon, first described by Fowler,1 has been known for over two decades, but its practical significance has only recently been discovered. Otologists have long recognized that certain patients experience an abnormally rapid increase in loudness when the intensity of sound is raised above their impaired threshold, but for many years it was thought that this recruitment was the inevitable accompaniment of all perceptive, as opposed to conductive, hearing loss.
The discovery by Dix, Hallpike, and Hood2 that recruitment is present only in lesions of the sensory receptor mechanism, i. e., hair cells and organ of Corti, has, in general, precipitated a renewed interest in this remarkable phenomenon, and, in particular, has emphasized the need for a simple, easily administered test of recruitment for clinical purposes. It has been recognized that such a tool would constitute a valuable addition to the otologist's armamentarium by allowing
JERGER JF. DL DIFFERENCE TESTImproved Method for Clinical Measurement of Recruitment. AMA Arch Otolaryngol. 1953;57(5):490–500. doi:10.1001/archotol.1953.00710030513002