Sound and visual urgency should tell the same story about risk level, not two different ones
Aliases: multimodal priority coding · auditory alarm coding · multimodal alarm
What it is
Multimodal priority coding aligns auditory urgency, visual salience, and persistence so that sound and vision express the same risk level consistently rather than telling separate stories. This leaf is about how the two channels should coordinate when encoding priority; what content fields a message should contain and how state should change after acknowledgement belong to the other two leaves in this group. Sound pulls attention outside the operator's current line of sight, while vision localizes the object and sustains identification; their functions differ, but their judgment about urgency for the same event must never conflict.
Why it happens
Consistent multimodal signals speed up orientation and provide redundancy under noise, occluded sightlines, or color-vision difference — even if one channel fails, the other still conveys the correct level. But when every piece of equipment defines its own alarm sound, or flashing is used regardless of actual state, operators cannot learn a stable mapping; sound and vision end up masking each other instead of jointly conveying a real level, which wastes coding capacity on inconsistent detail rather than using it to communicate urgency.
Where it stops holding
Exact sound pressure levels, colors, and flash rates are constrained by sector standards, ambient noise on site, lighting conditions, the use of hearing protection, and photosensitivity risk in some individuals from high-frequency flashing — a scheme validated at one site cannot simply be copied onto another environment unchanged. Once an alarm is acknowledged, the auditory cue may stop, but as long as the trigger condition has not actually cleared, the visual "unresolved" indication must remain; acknowledgement must not silently remove the visual cue along with the sound.
Applying it
Define a small, risk-analysis-derived set of cross-modal priority levels and timbre families, so that higher levels raise both auditory urgency and visual salience together. Test whether the scheme remains audible, discriminable, and localizable under real site noise levels, the actual distance between operator and alarm source, night-shift ambient brightness, and different color-vision conditions, and specifically check whether a high-priority alarm can be masked by the sound or light of concurrent lower-priority alarms.