Perceived Urgency

The subjective sense of immediacy or threat conveyed by an alert, shaped by parameters such as pulse rate, inter-pulse interval, pitch, loudness, and — for tactile signals — vibration intensity and pattern duration. Research on aircraft alarms, hospital alarms, and driver warnings has shown that perceived urgency scales predictably with these parameters, and this body of work is routinely drawn on by assistive-technology designers to encode two or three urgency levels (e.g., low-urgency warning when a collision becomes possible, high-urgency emergency when one is imminent) into the same audio or vibration channel without using speech.