Licking User Interface Design Hurdles

When you think about wearable electronic devices, chances are your mind will turn to thoughts of smartwatches, wristbands, glasses, and maybe even earbuds and on-skin patches. These are among the most explored options, but they are by no means the only ones. Consider the tongue, for example. Comparatively little work has gone into developing tongue-based interfaces, but this area of the body offers many unique characteristics that can be exploited. Because the tongue is densely innervated and highly electrically conductive, it allows for the discrimination of even closely spaced mechanical or electrotactile stimulation. And of course the taste receptors can be stimulated to produce taste sensations, which can make for highly immersive virtual reality experiences.

Existing tongue interfaces overwhelmingly focus on exploiting the ability to produce taste sensations, leaving the possibilities for tactile feedback largely unexplored. Similarly, using the tongue to interact with in-mouth input devices has received minimal attention from developers. These shortcomings are further exacerbated by the fact that most existing interfaces are very low in resolution, often containing only a single electrode. Moreover, there is generally no toolkit available to simplify developing devices with these interfaces. As such, extensive knowledge in electrical engineering and haptics is a prerequisite, which keeps the systems out of reach for many developers.

With a toolkit that is simpler to use, and that is capable of providing high-resolution feedback, this technology could be expanded into more mainstream use cases. That is exactly what a group of researchers at the University of Calgary and the University of Maine are trying to build. Their platform, called TactTongue, consists of a high-resolution electrotactile prototyping platform that was designed for use with the tongue. The team has also created a design tool that abstracts all of the low-level details of the system to allow developers to focus on higher-level objectives.

The TactTongue hardware platform consists of an array of eighteen electrodes that can render spatiotemporal tactile effects on the tongue with precision. This thin device, which sits at the end of a ribbon cable that is inserted into the mouth, could be used for both outputs and inputs. Controlled patterns of electrical stimulation can simulate the sensations of touch and, in some limited ways, taste. Further, by attaching the electrode array to the hard palate region of the mouth, moving the tongue across the electrodes can turn TactTongue into an input device that can be used when the hands are occupied, or for motor-impaired users.

The sensing portion of the platform interfaces with an Arduino Uno or Nano microcontroller development kit, which is much simpler to program than most existing solutions, allowing for the rapid iteration of prototypes, even when developers have no previous experience with haptics. This decision also significantly reduced overall component counts and kept costs low.

This simplified hardware platform pairs with a design tool that hides many low level details. It provides methods to, for example, control the individual electrodes or trigger a set of predefined spatiotemporal stimulation patterns with just a few clicks. This tool was designed to communicate directly with the Arduino board via its serial port.

To demonstrate the utility of the TactTongue platform, the researchers developed a number of applications, focusing initially on accessibility, medicine, and extended reality. The versatility exhibited in these demonstrations highlighted the system’s ability to leverage the unique characteristics of the tongue while while allowing for the rapid development of novel user interfaces.

Looking to the future, the researchers plan to spend some time assessing the likelihood of TactTongue to overstimulate nerves, which could result in sensory fatigue, with the goal of mitigating this risk. They also intend to further investigate individual variability in sensations which could ultimately result in more realistic experiences. It is hoped that TactTongue, and these enhancements, will enable new opportunities for the deployment of tongue-based interfaces.