Redundant Coding - Individual Sensitivity Differences

Designing displays for more than one sense modality is preferred because people vary widely in visual, auditory, smell, and touch sensitivities. As with color displays and accommodation for color-blindness, other sensory displays should incorporate redundant coding to accommodate individual differences.

In elevators, braille labeling (touch) of floor buttons and voice annunciation (auditory) systems are used to assist the visually impaired. Emergency vehicles use both flashing lights (visual) and sirens (auditory) to signal approach. Devices are available for those with smell impairments that both sound an auditory alarm and provide a visual readout in the event of a natural gas leak.

	Some train and subway platforms use both visual and tactile displays to indicate the platform edge. Yellow is used to visually convey "caution" for the sighted. Tiles with a special tactile surface are used to warn the visually impaired. (Armor-Tile photo)
Some home alarms for natural gas provide redundant coding for those with smell impairments who may not be able to smell the "mercaptan" additive. Our sense of smell can be temporarily affected by a cold or allergy or not available because we are sleeping. (Nighthawk photo)