This is a survey article on the information transmission capability of haptic devices and ways of maximizing it. It is intended for readers who are engineering professionals interested in developing novel haptic interfaces for a variety of applications but are not necessarily trained in haptic science or human user research. We posit that the ultimate goal of any interface is the exchange of information between a machine and a user, and as such, the evaluation should involve estimating the information-transmission capability with human users. We conducted a literature survey on studies of haptic devices evaluated with human users using an information theoretic framework. Our goal was to discover and summarize best practices that can lead to high information transmission. The results confirmed findings from our own previous studies, uncovered new ways to effectively increase information transmission, and pointed to the need for broader dissemination of proper experimental methodology. We, therefore, present a concise yet comprehensive tutorial on psychophysical methodology for estimating information transfer (IT) and IT rate with humans, survey results on the typical IT achievable with haptic devices, and guidelines for maximizing information transmission with any human-machine interfaces. Although we focus on haptic systems, the information-theoretic framework, the psychophysical methods, and the guidelines presented in this article are applicable to other sensory modalities and multimodal interface systems also.

We present a study to examine one's learning and processing capacity of broadband tactile information, such as that derived from speech. In Study 1, we tested a user's capability to recognize tactile locations and movements on the forearm in the presence of masking stimuli and determined 9 distinguishable tactile symbols. We associated these symbols to 9 phonemes using two approaches, random and articulation associations. Study 2 showed that novice participants can learn both associations. However, performance for retention, construction of words and knowledge transfer to recognize unlearned words was better with articulation association. In study 3, we trained novel participants to directly recognize words before learning phonemes. Our results show that novel users can retain and generalize the knowledge to recognize new words faster when they were directly train on words. Finally, Study 4 examined optimal presentation rate for the tactile symbols without compromising learning and recognition rate.

In our daily lives, we rely heavily on our visual and auditory channels to receive information from others. In the case of impairment, or when large amounts of information are already transmitted visually or aurally, alternative methods of communication are needed. A haptic language offers the potential to provide information to a user when visual and auditory channels are unavailable. Previously created haptic languages include deconstructing acoustic signals into features and displaying them through a haptic device, and haptic adaptations of Braille or Morse code; however, these approaches are unintuitive, slow at presenting language, or require a large surface area. We propose using a multi-sensory haptic device called MISSIVE, which can be worn on the upper arm and is capable of producing brief cues, sufficient in quantity to encode the full English phoneme set. We evaluated our approach by teaching subjects a subset of 23 phonemes, and demonstrated an 86% accuracy in a 50 word identification task after 100 minutes of training.