Sensory Feedback Technology

With PSYONIC's technology we are able to give both touch and joint location sensing back to the user.

Touch & Pressure

In providing touch feedback, we place pressure sensors in the hand that are relayed to the user through electrical stimulation of the skin. By doing this, the user feels vibration, tingling, or pressure when he touches an object. In order to mitigate the problem of the user potentially getting shocked during long-term wear of our stimulation device, we developed an algorithm in our lab that monitors the impedance of the electrode-skin interface, which is indicative of how well an electrode is contacting and conducting across your skin. When the contact is poor, we’re able to adjust the total amount of current delivered across the skin such that the user feels a constant sensation intensity at all times.

A. Akhtar, J. Sombeck, J. Cornman, S. Goldfinger, T. Bretl. Realtime electrotactile force feedback from a finger prosthesis using a low-cost pressure sensor. Demo. World Haptics Conference, Chicago, IL, 2015.

A. Akhtar, B. Boyce, T. Bretl. The relationship between energy, phase charge, impedance, and perceived sensation in electrotactile stimulation. Proceedings of IEEE Haptics Symposium, Houston, TX, 2014.


We provide proprioception by attaching a small plastic pad to the forearm and coupling it with a finger. As the finger is flexed the pad pulls the skin on the forearm, letting the user know the position of the finger based on this feedback. In a study we published from our lab, we presented 6 different grasps to subjects. They were blindfolded and acoustically shielded, and after only 6 minutes of training, they were able to distinguish between the grasps with over 88% accuracy, based off of feeling skin stretch alone. Imagine how well they would do after weeks of using the device.


A. Akhtar, M. Nguyen, L. Wan, B. Boyce, P. Slade, T. Bretl. Passive mechanical skin stretch for multiple degree-of-freedom proprioception in a hand prosthesis. Proceedings of EuroHaptics, Versailles, France, 2014.



The vast majority of commercial hands only open and close. We employ pattern recognition algorithms that allow the user finer control, so that they can additionally do finger pinching and three finger grasping, which is necessary in everyday life.

Pinch grasp

The pinch grasp uses the index and thumb to maneuver small objects such as this battery, a penny or even a pencil.


The three finger grasp employs the index, thumb and middle finger to hold onto larger objects such as a bottle cap. 



This is the most basic grasp offered. The power grasp can be used for anything from shaking hands to grabbing a cereal box for breakfast. 



This grip is similar to the power grip except the index finger slowly lags behind the rest in order to grip a drill and then engage it after. 



This grip is also very similar to the power grip except for the thumb comes out to the side in order to hold a key as shown in the picture. This grasp can also be used to participate in a very unfair game of thumb war. 

P. Slade, A. Akhtar, M. Nguyen, T. Bretl. Tact: design and performance of an open-source, affordable, myoelectric prosthetic hand. International Conference on Robotics and Automation, Seattle, WA, 2015.

J. Jeong, W. Yeo, A. Akhtar, J. Norton, Y. Kwack, S. Li, S. Jung, Y. Su, W. Lee, Y. Huang, W. Choi, T. Bretl, J. Rogers. Materials and optimized designs for human-machine interfaces via epidermal electronics. Advanced Materials, 2013.