A new paradigm for the design of audible alarms that convey urgency information

The current international standard (IEC 60601-1-8) stipulates that medical device audible alarms should be priority-encoded and validated for efficacy. Evidence suggests that the melodic alarms described in the standard are not functioning as originally intended. We present a multi-disciplinary, human factors paradigm for audible alarm development whereby urgency information is encoded via modulation of the physical characteristics of sounds. We also test the feasibility of this approach using information measures.

We designed series of experimental sounds that varied along controlled physical and acoustical dimensions. Subjects rated these sound series for perceived urgency. Based on these ratings, selected sounds from each series were assigned a priority category from 'low' to 'high' - we call these resulting sets of sounds 'urgency-codecs'. The method of categorical judgments (based on information theory) was used to compare each urgency-codec for ability to convey urgency information.

Subjects were consistent in their ratings of the three series of experimental sounds for perceived urgency. The urgency data pertaining to one of the series (harmonic interval) was successfully fit to a psychophysical empirical law. The urgency-codec derived from another sound series (melodic interval) was found to have the highest signal (correct interpretation of urgency level by subjects) transmission rate.

The proposed paradigm is feasible, and it offers an evidence-based strategy for alarm sound design and testing. This approach would be performed before implementation of new alarm sounds in clinical settings, and should result in development of alarm sounds that satisfy the requirements of priority-encoding and validation.