History and Lingering Impact of the Arbitrary 25-dB Cutoff for Normal Hearing

Abstract

Purpose Since its inception nearly a century ago, the audiogram has become the gold standard for reporting an individual's hearing status. The interpretation of the audiogram, namely, where normal hearing ends and hearing loss begins, impacts all areas of audiology: research, clinical, and medicolegal. Where to define normal hearing was the subject of great debate during the early decades of audiology. Revisiting this history reveals how the 25-dB HL cutoff came to be; a decision concerned more with the legal consequences than the scientific persuasiveness of the definition of normal hearing. Since the 1970s, the 25-dB HL cutoff has defined normal-hearing control groups in research and informed treatment recommendations in the clinic. Conclusions Today, in 2020, closer evaluation of this so-called normal-hearing group reveals a variety of deficits not captured by the audiogram. The history of how normal hearing came to be defined in conjunction with this growing body of research serves as a good reminder to look beyond the audiogram. This is especially important as the field of audiology looks ahead toward improved diagnostics, earlier detection, and new technologies/treatments.