Tactile Vision Substitution System

Innovation and OT


Low vision exists on a spectrum ranging from impaired vision to low light perception and complete blindness. While low vision is defined as “having 20/40 or worse vision in the better eye even with eyeglasses”1, low light perception is having difficulty to tell dark from light and the general direction of a light source2. Many assistive devices exist for individuals with low vision. In a study, the participants identified 124 different low vision assistive devices (LVAD)3. The LVAD that are most effective for individuals with low vision are most often devices for spot reading tasks, such as magnifiers and closed-circuit television, and for finding objects such as bump dots and talking devices4. However, individuals who utilize an assistive device for mobility continue to have difficulty with tasks that require reading or interpretation of signs, such as bathroom and exit signs, when navigating in the environment3.

A new LVAD that could potentially fill the gap for sign reading and object recognition is a tactile vision substitution system. One form of noninvasive tactile vision substitution is a tongue display unit (TDU), which is a form of portable sensory substitution that uses tactile sensation to substitute for the absence visual sensation. A TDU consists of a pair of glasses with a camera and wire that connects to a square array placed on the user’s tongue. With training, the user learns to interpret the “images” display on the tongue. Hence, an intact optical nerve tract is not required to use a TDU. And there is emerging evidence that a TDU may improve words and object recognition, and path finding for individuals with low vision of light perception or less.

Tongue Display Unit (TDU) and Functional Task Performance

A study by Nau, Pintar, Arnoldussen, & Fisher explored the use of TDU for functional task performance in individuals with low vision of light perception or less5. TDU training was provided in a sensory substitution lab at least twice a day for three-hour sessions over three days. At home, participants were required to log a minimum of 300 minutes per month using the TDU to remain in the study. In this study, functional task performance was assessed using object identification and word identification tasks. For the object identification task, four objects were evenly spaced on a table with a contrasting cover. The four objects (a plastic banana, a coffee mug with handle, a yellow highlighter marker and a softball) were randomly placed in front of the participants in 20 trials. Participants were given 2 minutes to touch the indicated object or their trial would be scored as incorrect. In the word identification task, words were presented on a 17-inch monitor in white 95-point font on a black background. Selected words included bread, plant, tree, dress, moon, farm, ring, cup, dog, and bus. Participants were given three minutes to name the word correctly or their trial would be scored as incorrect. The functional task performance was assessed at 3-month, 6-month, 9-month, and 12-month follow-ups.

The study from Nau et al. demonstrated that with training and practice, participants successfully identified both objects and words with the TDU5. For object identification, chance level was set at 25%; after training and in a span of 15-20 trials, the participants correctly identified a range of 5-19 objects. Similarly, though word identification was considered near impossible before the use of a TDU, the participants read an average of 1.5 out of 10 words presented, and with a range of 0-10 words named correctly after training. Since some participants were having difficulty in reading words using the TDU, the authors concluded that more time and practice were necessary to identify various letter shapes, especially for those participants who were congenitally blind. Nevertheless, though the improvement in functional performance was not analyzed for statistical significance, there was still notably improvement in functional task performance with the use of a TDU. To apply this study to individuals in the larger low vision community, the authors recommended a more intensive training with ongoing home support for six months to a year post-training to facilitate successful use of a TDU in daily life5.

A different study by Grant et al. explored the impact of a TDU on functional task performance of object recognition, word recognition, and orientation and mobility (O&M) tasks in participants with profound blindness6. Ten hours of device training was provided to participants by an experienced TDU trainer. Participants were educated in how to control the device and learned how to interpret the tactile stimulation. Participants were also required to log a minimum of 300 minutes per month on their TDU for twelve months.

The three functional performance tasks were object recognition, word recognition, and O&M. To successfully complete the object recognition task, the participants had to use the TDU to locate and touch the target object placed in front of them within 2 minutes. The four objects placed on a black surface included a plastic banana, a coffee mug, softball, and a highlighter marker. Twenty trials with a randomized target object as well as order of objects were completed. For word recognition, the participants sat 50 cm from a 17-inch computer monitor and were required to read words, presented one at a time, within 3 minutes for each word. Ten selected words (dog, cup, moon, bus, ring, farm, dress, tree, plant, and bread) were presented to the participants in a random order. As for the O&M task, the participants were required to navigate down a hallway and touch a sign on the wall in less than 10 minutes on their first attempt. The researchers found statistically significant improvement in the object recognition and O&M tasks, and there were no significant differences found between participants with congenital blindness versus participants with acquired blindness6.

The researchers also found that even with as little as ten hours of basic training in the use of the TDU, the participants were able to identify objects and words, as well as navigate in a hallway without the use of a cane or guide dog. Therefore, the researchers concluded that the TDU could facilitate occupational performance of object recognition, word identification, and O&M tasks after skilled training from a professional6.

Impact on Occupation

Both studies demonstrated that a TDU may have the potential to positively impact occupational participation by allowing individuals with vision less than light perception to recognize and identify objects, words and signs in daily life. Hence, a TDU can possibility enable individuals with vision less than light perception to complete occupations such as locating food items in supermarket, avoiding gross hazard in the environment or even reading a simple menu in a restaurant. However, successful incorporation of cutting edge technology, such as the TDU, into daily living tasks depends on skillful training from professionals who are experts in activity analysis and gradation of activities. Occupational therapists have the knowledge and skills to provide the needed training and ongoing support service to integrate TDU into daily living tasks. Hence, it is important for occupational therapists to keep in pace with innovative technological development through knowledge and use of the newest technology to impact occupation and improve quality of life of our clients.


  1. Blindness and Vision Impairment| Gateway to Health Communication | CDC. Cdcgov. 2016. Available at: http://www.cdc.gov/healthcommunication/ToolsTemplates/EntertainmentEd/Tips/Blindness.html. Accessed August 30, 2016.
  2. Duffy M. Low Vision – VisionAware. Visionawareorg. 2016. Available at: http://www.visionaware.org/info/your-eye-condition/eye-health/low-vision/low-%20vision-terms-and-descriptions/1235#LightPerception_and_LightProjection. Accessed September 2, 2016.
  3. Fok D, Polgar JM, Shaw L, Jutai JW. Low vision assistive technology device usage and importance in daily occupations. Work. 2011;39(1):37-48. doi:10.3233/WOR-2011-1149
  4. Stelmack J, Rosenbloom A, Brenneman C, Stelmack T. Patients’ perceptions of the need for low vision devices. Journal of Visual Impairment & Blindness, Sep2003; 97(9): 521-535.
  5. Nau A, Pintar C, Arnoldussen A, Fisher C. Acquisition of Visual Perception in Blind Individuals Using the BrainPort Artificial Vision Device. American Journal of Occupational Therapy. 2014;69(1):6901290010p1. doi:10.5014/ajot.2015.011809.
  6. Grant P, Spencer L, Arnoldussen A, et al. The functional performance of the BrainPort V100 device in persons who are profoundly blind. Journal of Visual Impairment & Blindness. March2016;110(2):77-88.

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