Table 1 Guiding principles for the implementation of sensory feedback in upper-limb prostheses

The sensory feedback system should enable the user to trust it.

\(\bullet\) The features of the sensory feedback system should be communicated clearly in terms of sensation quality, sensitivity and area covered.

\(\bullet\) Feedback sensation should not be influenced by external factors (e.g. arm position).

\(\bullet\) The sensory feedback system should be durable.

\(\bullet\) The sensor locations should cover all of the areas used to hold objects (i.e not just the fingertips).

\(\bullet\) The calibration and settings adjustment options should be designed to ensure reliability (e.g. have simple and advanced options to ensure the saved setup is not deleted by mistake).

Sensory feedback should be comfortable for long-term use.

\(\bullet\) The system should allow the user to adjust the feedback intensity and extent (i.e. how much feedback they want).

\(\bullet\) The feedback should not be intrusive when objects are held for a long time.

\(\bullet\) The weight of the system should be negligible.

\(\bullet\) The user should be able to switch the feedback off easily (e.g. button on the prosthesis rather than through an app).

Sensory feedback should not have a negative impact on normal prosthesis use.

\(\bullet\) Sensory feedback should not distract from other activities (e.g. introduced gradually to allow the user to get accustomed to it).

\(\bullet\) Sensory feedback should complement other implicit feedback sources.

\(\bullet\) Sensory feedback should integrate with existing notifications available through the arm (to not be confusing).

Sensory feedback should not draw extra attention.

\(\bullet\) Sensory feedback should not be audible.

\(\bullet\) The design of the sensory feedback system should either be integrated into the prosthesis or hidden without adding bulkiness (as that would cause difficulties with long-sleeve clothing).

The feedback should not interfere with the user’s acceptance of limb difference.

\(\bullet\) The way sensory feedback is described should be appropriate to its capabilities (e.g. tactile feedback for vibrotactile feedback).

\(\bullet\) The language used should be appropriate with the fact that the prosthesis is a tool and is not attempting to replace a body part (e.g. instead of asking how “natural” the sensation felt, could ask how “comfortable” it was).