What is its next action? Legibility of intent
Legibility, the ability to understand what a system is about to do, is critical for collaboration and safety. In digital interfaces, this is largely achieved through text, as well as visual state changes. For physical AI, intent must often be conveyed through non-verbal signals because of practical limits on communication and speed needs in dynamic environments. Legibility is the new usability.
Physical AI should use a combination of visual, auditory and haptic signals to communicate intent. Examples include:
- Visual: lights that change color to indicate states (e.g., sensing, deciding, acting), or projected arrows showing movement direction
- Auditory: tones or spoken alerts for critical actions, in addition to speech for more detailed communications
- Haptic: vibrations on wearable devices for proximity warnings
Signals must be salient under real-world conditions. Consider line-of-sight, ambient noise and human perceptual capabilities. Redundant cues (e.g., combining lights and sounds) improve reliability in noisy or visually cluttered environments. Testing these signals under real-world conditions is essential to ensure they remain effective when attention is divided.
Borrowing from human-to-human interactions, the system can use “gaze” direction (direction of optical sensors), posture (articulation) and motion pacing (cadence of movement) to indicate intent. For instance, slowing down before turning can signal caution, much like human body language. These cues feel natural and reduce cognitive load.
Like onboarding, legibility is bidirectional. Physical AI must interpret human signals like speech, gestures and movement to ensure safe and collaborative operation. This mutual understanding forms the foundation of safety and trust in shared spaces and rapid activity.
How certain is it in its actions? Level of confidence
As physical AI operates in real space where errors can have tangible consequences, confidence signaling is essential. Systems should not act when certainty does not meet a prescribed threshold, but acting with reduced confidence may be necessary and useful when learning new tasks or dealing with novel situations.
Co-workers need to know when the system is uncertain before it acts. Low-confidence actions could lead to collisions, dropped objects or privacy breaches. Communicating uncertainty allows humans to attend to, and intervene, proactively and prevents small errors from cascading into major failures.
As with signaling intent, confidence signals should be immediate and multimodal. In fact, intent and confidence should be a combined communication where appropriate. They should also scale with risk so that, the higher the potential impact, the more prominent the signal. For example, a high confidence action could be done at normal speed paired with a solid green light and slow pulsed sound. When confidence is below a set threshold (but above a minimum for allowable action), the task can occur at a reduced speed with a flashing amber light and higher frequency sound to signal relative uncertainty and provide more time for human redirection.