Implanted User Interfaces

Christian Holz, Tovi Grossman, George Fitzmaurice and Anne Agur. CHI 2012.

Introduction

We have experienced an obvious transition of computing to mobile devices: we communicate and access information on our mobile devices, anytime and anywhere. At the same time, there has been another transition, one that has been far less obvious. People have started to receive implanted devices for medical purposes, such as pacemakers and hearing aids.

Such implanted devices along with the information they store always travel with the user; there is no need for manually attaching them and the user can never forget or lose them. Thus, implanted devices are available at all times. While they are invisible to other people, over 3 million people have implanted pacemakers alone.

However, to check on their own status, a user needs to see a physician—the user is not able to directly interact with the implanted device themselves. Since it is unclear how a user might interact with an implanted device directly, we explored the four core areas of interfaces that implanted devices provide: accepting input from the user, providing output to the user, communicating wirelessly with external devices, as well as wireless powering.

Figure 1

Implanted User Interfaces: Figure 1

Implanted user interfaces allow users to interact with small devices through human skin. (a-b) This output device is implanted (c) underneath the skin of a specimen arm. (d) Actual photograph of the LED output through the skin. (e) This standalone prototype senses input from an exposed trackball (f) and illuminates it in response.

Abstract

We investigate implanted user interfaces that small devices provide when implanted underneath human skin. Such devices always stay with the user, making their implanted user interfaces available at all times. We discuss four core challenges of implanted user interfaces: how to sense input through the skin, how to produce output, how to communicate amongst one another and with external infrastructure, and how to remain powered. We investigate these four challenges in a technical evaluation where we surgically implant study devices into a specimen arm. We find that traditional interfaces do work through skin. We then demonstrate how to deploy a prototype device on participants, using artificial skin to simulate implantation. We close with a discussion of medical considerations of implanted user interfaces, risks and limitations, and project into the future.

Publication

Christian Holz, Tovi Grossman, George Fitzmaurice, Anne Agur. 2012. Implanted User Interfaces. In Proceedings of the 2012 annual conference on Human factors in computing systems (CHI '12). Austin, TX, USA (May 5-10, 2012). ACM, New York, NY, USA, 503–512.
@inproceedings{holz2012,
	 author = {Holz, Christian and Grossman, Tovi and Fitzmaurice, George
                   and Agur, Anne},
	 title = {Implanted user interfaces},
	 booktitle = {Proceedings of the 2012 ACM annual conference on
                      Human Factors in Computing Systems},
	 series = {CHI '12},
	 year = {2012},
	 isbn = {978-1-4503-1015-4},
	 location = {Austin, Texas, USA},
	 pages = {503--512},
	 numpages = {10},
	 url = {http://doi.acm.org/10.1145/2207676.2207745},
	 doi = {10.1145/2207676.2207745},
	 acmid = {2207745},
	 publisher = {ACM},
	 address = {New York, NY, USA},
	 keywords = {augmented humans, disappearing mobile devices,
                     implantables, implanted devices, implanted interfaces,
                     mobile devices, wearable computing, wireless power},
}

Figures

Figure 2: Prototype implant and artificial skin

Implanted User Interfaces: Prototype implant and artificial skin

We covered a prototype device (a) with a layer of artificial skin (b) to collect qualitative feedback from use in an outdoor scenario. Participants received output triggers through the artificial skin and responded with input.

Figure 3: Implanted devices

Implanted User Interfaces: Implanted devices

These devices were implanted during the study. Plastic bags around devices prevent contact with tissue fluid.

Figure 4: Study setup with input apparatus set up

Implanted User Interfaces: Study setup with input apparatus set up

A piston repeatedly dropped from controlled heights onto the sensors.

Figure 5: Illustration of skin layers

Implanted User Interfaces: Illustration of skin layers

All devices were implanted between the skin and the subcutaneous fatty tissue.

Figure 6: Results for the force sensor

Implanted User Interfaces: Results for the force sensor

On average, skin accounts for 3N overhead for impact forces on pressure and touch sensors.

Figure 7: Results for the button

Implanted User Interfaces: Results for the button

The piston activated the button from all tested heights in the baseline condition, but activated the button reliably only from a height of 1cm and up when implanted.

Figure 8: Results for brightness and capacitive sensor

Implanted User Interfaces: Results for brightness and capacitive sensor

(left) Impact on sensed brightness and on sensed capacitance (right). Curves average the values of all five trials.

Figure 9: Setup of external light sensor (DSLR camera) and vibration sensor (accelerometer)

Implanted User Interfaces: Setup of external light sensor (DSLR camera) and vibration sensor (accelerometer)

a) A camera captured the intensity of produced light and (b) an accelerometer measured vibration intensities.

Figure 10: Results for minimum perceivable light and vibration output

Implanted User Interfaces: Results for minimum perceivable light and vibration output

(left) Minimum perceivable LED intensity. (right) The accelerometer did not pick up a signal through skin at motor intensities of 40% and lower. Dotted lines indicate the participant’s absolute perception thresholds.

Figure 11: Results for minimum perceivable audio output

Implanted User Interfaces: Results for minimum perceivable audio output

Sound perception through skin is possible, but skin substantially takes away from the output intensity (left). This effect grows with the distance between listener and speaker (right). Dotted lines indicate absolute perception thresholds.

Figure 12: Results for the measured audio levels underneath skin

Implanted User Interfaces: Results for the measured audio levels underneath skin

The differences in perceived sound intensities were nearly constant between the implant and the baseline session.

Figure 13: Setup of the wireless charging apparatus

Implanted User Interfaces: Setup of the wireless charging apparatus

The wireless charging mat docks to the receiver, which is implanted inside the specimen.

Figure 14: Results for the inductive charging device

Implanted User Interfaces: Results for the inductive charging device

Skin affected the current provided through the wireless connection only at higher current values.

Figure 15: Results for wireless communication throughput and speed

Implanted User Interfaces: Results for wireless communication throughput and speed

(left) Bluetooth exchanges data reliably when running slow, but comes with data loss when running fast. (right) Implanting affected fast transmission rates negatively.

Figure 16: Artificial skin prototypes

Implanted User Interfaces: Artificial skin prototypes

Artificial skin, created from silicon, covered the 3in3out device to simulate implantation and allow for testing.