Visual Detection of Detectable Warning Materials by Pedestrians with Visual Impairments - Final Report

2.4 False Detections

On each of the white, brown, and asphalt side walks, each participant experienced two trials in which there was a flat blank panel on the sidewalk instead of a bumpy detectable warning. Out of 300 total blank trials, 11 (3.7 percent) resulted in “false alarms” or false detections where the participant reported seeing a detectable warning even though the target was a blank panel. Nearly half of the false detections were due to a single participant who reported seeing a detectable warning on 5 out of 6 of her blank trials. This participant’s results indicate that she responded appropriately to the actual detectable warnings despite the false detections on blank trials. If her data are set aside, the false alarm rate for the remaining group of 49 participants was 2 percent. The low false alarm rate is consistent with the instructions to participants to report that they could see a detectable warning when they were “confident” that there was a detectable warning on the sidewalk.