Approaching from behind causes discomfort
Aliases: rear approach · out-of-view approach · approach from behind
What it is
Rear-approach discomfort is the startle, vigilance, and loss of control produced when a robot closes distance outside a person's field of view. The operative issue is not the compass direction itself but the absence of continuous visual tracking until sound, airflow, or peripheral appearance reveals the robot.
Why it happens
A visible approach supports continuous estimation of range, speed, and intent. From behind, prediction depends on unreliable auditory cues; in noise or with a quiet platform, detection can occur with little time remaining. Sudden appearance elicits orienting and startle, while close following may be interpreted as pursuit or intrusion even when collision separation is technically satisfied.
Studying it
Approach direction, speed, preview cue, and ambient noise can be crossed while measuring first detection, turning, startle, stop requests, closest distance, and comfort. Researchers should verify that the robot was genuinely unseen and limit repeated-trial anticipation. Field observation adds realistic distraction but provides weaker causal attribution.
Where it stops holding
Rear positioning can be appropriate in queues, load-following, or explicitly negotiated following. A continuous low-intensity cue and user control can reduce surprise, but audio cannot serve people with hearing loss or headphones. In a constrained passage, waiting is preferable to using a stronger alert as permission to squeeze past.
Applying it
- Prefer routing into side-front visibility. If impossible, give a directional cue before entering personal space.
- Do not assume audio is available; combine visible cues, floor projection, or waiting.
- Test while participants perform realistic distracting tasks. Measure detection distance and braking margin after they turn; prohibit the route if the remaining margin is insufficient for interpretation and avoidance.