Abstract

This review highlights the biomechanical foundations of braille and tactile graphic discrimination within the context of design innovations in information access for the blind and low-vision community. Braille discrimination is a complex and poorly understood process that necessitates the coordination of motor control, mechanotransduction, and cognitive-linguistic processing. Despite substantial technological advances and multiple design attempts over the last fifty years, a low-cost, high-fidelity refreshable braille and tactile graphics display has yet to be delivered. Consequently, the blind and low-vision communities are left with limited options for information access. This is amplified by the rapid adoption of graphical user interfaces for human-computer interaction, a move that the blind and low vision community were effectively excluded from. Text-to-speech screen readers lack the ability to convey the nuances necessary for science, technology, engineering, arts, and math education and offer limited privacy for the user. Printed braille and tactile graphics are effective modalities but are time and resource-intensive, difficult to access, and lack real-time rendering. Single- and multiline refreshable braille devices either lack functionality or are extremely cost-prohibitive. Early computational models of mechanotransduction through complex digital skin tissue and the kinematics of the braille reading finger are explored as insight into device design specifications. A use-centered, convergence approach for future designs is discussed in which the design space is defined by both the end-user requirements and the available technology.

1 Introduction

Recent 2020 Vision Atlas estimates suggest that 1.1 billion people of all ages globally are living with vision loss. Of these, an estimated 43 million people are blind (0.5% prevalence) and another 295 million people have moderate to severe vision impairment (3.7% prevalence). In the United States alone, there are an estimated 16 million people with vision loss (5.0% prevalence), of which 640,000 people are blind (0.2% prevalence) [1]. The total United States estimated economic burden of vision loss and blindness was $134.2 billion, of which $35.5 billion are attributed to indirect costs, such as absenteeism, reduced workforce participation, lost household production, and informal care. Furthermore, an individual personally affected with vision loss or blindness spends an average of $16,838 annually in associated costs [2]. While vision loss is skewed to the aging population, according to the latest data from the National Survey for Children's Health, approximately 71,000 children aged 0–17 (1.57% prevalence) are blind or have problems seeing even when wearing corrective glasses [3].

According to the 2019 American Printing House for the Blind Annual Report, of all legally blind students registered in precollege educational settings, 8.4% use braille as their primary reading medium, 32.9% primarily use vision, 10.2% primarily use auditory readers, 18.1% are prereaders, and 30.4% are symbolic or nonreaders (Fig. 1) [4]. While braille literacy rates are declining for reasons including lack of braille educators, lack of access to braille materials, and increasing use of text-to-speech technology [5], braille literacy remains a predictive factor in employment outcomes for the blind and low vision community. A 2018 survey found a higher employment rate among adults who used braille at least once a week (65%) when compared to adults who did not (45%) [6]. Furthermore, braille literacy has been shown to significantly improve overall quality of life [5].

Fig. 1
Predominant reading modality of precollege students
Fig. 1
Predominant reading modality of precollege students
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Efforts to increase braille literacy have focused on increasing access to braille materials, improving braille education, and advancing current and emerging braille technologies [7]. Increasing access to braille materials is especially challenging given the time- and resource-intensive nature of producing braille, especially within STEM subjects, where complex equations and graphical or spatial representations are integral to understanding the material. While the data are sparse, first-edition braille mathematical textbooks have been documented to cost anywhere from several thousand dollars to $30,000 and can take six to twelve months or more for transcription [8,9]. The AMAC Accessibility Solutions and Research Center at Georgia Tech, one of a handful of national braille printing presses, reported that it receives approximately 400 orders for braille textbook transcriptions per year, including STEM texts [10]. This could result in up to $12 million in associated costs. Furthermore, despite best efforts at procuring braille texts, due to the time-intensive transcription process, some materials may arrive after the student has already completed the course [8]. Herein, we will discuss the historical development of braille technology and tactile displays and the role that biomechanical analysis will play in the future advancement of refreshable systems for the blind and low-vision community.

2 Background

Printed braille text was developed in 1824 by Louis Braille and was designed to serve as a universal reading and writing system for use by blind or visually impaired people [1114]. Braille text was derived from the Barbier system which was a 12-dot system French soldiers used to communicate at night without making noise [14,15]. Traditional braille cells consist of six dots and are two dots wide and three dots high. An alternative version of braille, the 8-dot system, consists of eight dot cells that are two dots wide and 4 dots high. The current 6-dot system allows for 64 possible dot combinations whereas the 8-dot system allows for 256 possible dot combinations. There are two primary types of braille: uncontracted (grade 1) and contracted braille (grade 2). Uncontracted braille is a very basic form of braille, generally used by beginners. It requires a considerable amount of space because every word is spelled out letter by letter. Typically, uncontracted braille takes less than 4 months to learn [16]. Contracted braille is more complex and is used by more experienced braille users. It makes use of abbreviations and contractions, to shorten words and increase the speed of reading and writing. This form of braille can take up to two years to learn [16]. Along with contracted and uncontracted braille, there are two systems used to communicate mathematical and scientific notation, Unified English Braille (UEB) and the Nemeth Braille Code. Printed tactile graphics that often incorporate braille provide an interpreted version of data plots, photographs, paintings, and other visual images [17,18], often requiring considerable time and effort to generate (Fig. 2). More recent advances include the use of three-dimensional printed objects that can accompany the printed braille.

Fig. 2
Designers from the Clovernook Center for the Blind and Visually Impaired (Cincinnati, OH) developed tactile graphic renderings of a painting (a), sculpture (b), and a Campbell's soup logo (c), demonstrating many of the challenges associated with creating tactile images. The relevant details must be extracted, converted to grayscale images, and then stylized to ensure that they can be printed. The features that appear gray in the stylized images exhibit a roughened texture.
Fig. 2
Designers from the Clovernook Center for the Blind and Visually Impaired (Cincinnati, OH) developed tactile graphic renderings of a painting (a), sculpture (b), and a Campbell's soup logo (c), demonstrating many of the challenges associated with creating tactile images. The relevant details must be extracted, converted to grayscale images, and then stylized to ensure that they can be printed. The features that appear gray in the stylized images exhibit a roughened texture.
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Clovernook Center for the Blind and Visually Impaired is the largest provider of embossed braille in the world. Of the 30 million pages they produce each year, most are delivered to public libraries and schools dedicated to teaching students with visual impairment. Unfortunately, the pages are many times thicker than a regular printed document such that the Oxford English Dictionary requires an entire bookshelf to hold a single braille copy. Consequently, it is difficult for most public libraries to maintain the large store of braille books required to meet a general education program's needs and even more challenging for schools to offer an array of textbooks to each learner.

The introduction of the Kurzweil Reading Machine in 1976 was revolutionary in that it integrated advanced optical character recognition software, a flatbed scanner, and screen reader software [19]. The resulting table-sized device could read any document placed under the scanner. Audio screen readers for personal computers were later developed by Jim Thatcher in 1986 and, as their name implies, they enable a computer-actuated voice to read the contents of the screen to an individual in a line-by-line fashion. Both technologies have since been integrated into many operating systems and online applications. Audio readers were anticipated to be revolutionary for the blind. But for a person learning physics, calculus, or how to program in Python or C++, it is necessary to interact with the text—something that is very difficult with an audio reader. For instance, it is challenging to understand complex equations read out loud and even more difficult to describe theorems in geometry or trigonometry without the aid of graphical representations. For multivariate calculus, audio readers can only provide a rough description of the critically important nuances associated with differentiation and integration, especially in multiple dimensions.

Single- and multiple-line refreshable displays have existed since the 1970s [20] although the first patent for such a device dates back to 1916 and was described by George Gordon Brown [21]. They can translate electronic text into braille text and update pin placement across 1–10 lines. These displays can update quickly and can produce rudimentary graphics. They typically use solenoids, piezo-electric actuators, or pneumatic devices to raise and lower the surface of the page. Refreshable, multiline displays have been invaluable because they can be used to read multiple books on the same system, alleviating the storage concerns associated with printed braille text. The primary challenge is that, to date, they have been designed primarily for text and, consequently, have very low resolution and limited use as tactile displays. The pin configurations resemble those of a dot-matrix printer and are unable to replicate the features of printed braille graphics even if they could be deployed across an entire page. Full-page graphics on multiline displays experience significant reliability challenges due to the many moving parts involved (at least 8,000 and up to 15,000 moving pins). They also require bulky and complicated control mechanisms that often operate at dangerously high voltages and consume considerable power [2224].

3 Refreshable Braille Displays

Although similar in design complexity and appearance, refreshable braille displays and tactile graphic displays are inherently different. Refreshable braille is intended for the purpose of reading single or multiple lines of braille text, while tactile graphic displays are intended to display spatial tactile graphics, such as rudimentary pictures, geometrical representations, charts, graphs, maps, etc.

Though the first refreshable braille device in the United States, the VersaBraille [25] was introduced to the market in 1979 by Telesensory Systems, it was a tactile graphic display that paved the way. The Optacon, Telesonsory Systems' debut device, demonstrated the feasibility and efficacy of a refreshable device. The Optacon was conceived by John Linvill, a professor of electrical engineering at Stanford University, whose daughter was blind. The Optacon is a vibrotactile stimulator that utilizes an optical scanner to convert any print materials font size 6 to 20 into a tactile representation of letters and symbols using a 24 × 6 array of piezo-electric bimorphs vibrating at 230 Hz [2629]. Patented in 1966 and available for sale in 1971, the device cost $3400 (equivalent to approximately $16,700 in 2023 dollars), but immensely increased access to print materials of all kinds, including text, basic graphics, mathematical equations, music, and allowed for unprecedented autonomy and privacy (Fig. 3) [27,30,31]. The second-generation Optacon II even had a specialized lens to allow for optical scanning of computer monitors [32]. As we will see with so many refreshable braille and tactile graphic devices, after 25 years in production and an estimated 15,000 units sold, Telesensory Systems discontinued the Optacon in 1996 to focus on more profitable products [33]. Despite this, there are still Optacon systems in use today [27].

Fig. 3
A demonstration of the Optacon optical to tactile converter. As the user scans the camera lens across print material, the image is converted to vibrotactile output on a 24 × 6 array of piezo-electric bimorphs. Courtesy of the Museum of the American Printing House for the Blind.
Fig. 3
A demonstration of the Optacon optical to tactile converter. As the user scans the camera lens across print material, the image is converted to vibrotactile output on a 24 × 6 array of piezo-electric bimorphs. Courtesy of the Museum of the American Printing House for the Blind.
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Eight years after the introduction of the Optacon, in 1979, Telesensory Systems would produce the first refreshable braille device in the United States, the VersaBraille, which drew upon the Elinfa Digicassette designed by Oleg Tretiakoff of Murac Micromatic in France and sold in France for $2600 [34,35]. The VersaBraille device has a Perkins-style 6-key keyboard and converts up to 400,000 braille characters stored on cassette to a braille display consisting of 20 6-dot braille cells. The advantages of VersaBraille over conventional paper braille were immense, including the capability for real-time editing, quiet, undisruptive reading and writing, increased writing speed rate, and more effective educational strategies among others. The downsides were size (too heavy for young students to carry), fragility (unable to withstand drops) and, as expected, cost [36]. Ultimately, despite being an undisputed leader in assistive technology for the blind and low vision community, Telesensory Systems abruptly filed for bankruptcy in 2005 [37]. Many of Telesensory Systems' experienced employees continued to work in the assistive technology field, for companies such as Kurzweil Technologies, HumanWare, Blazie Technologies (now merged with Freedom Scientific), and Freedom Scientific, producing the next generation of refreshable devices and information access technologies.

A major advancement for refreshable braille access in the United States, the introduction of the Elinfa and VersaBraille technology coincided with a rapid uptick of commercialized refreshable braille devices from various organizations (Fig. 4, Table 1), many of which were attempting to increase the number of braille cells and overall functionality but consistently utilized piezo-electric actuators. In 1975, Braillex was introduced in Germany by Papenmeier and consisted of a refreshable braille device with advanced indexing capabilities. The Braillocord BRS 76 was announced in 1976 by AID Electronik GmbH in Germany and sold for $3500. It had 32 refreshable braille cells that could input text from a cassette and also recall previous text for rereading [38,39]. The next decade of refreshable braille devices saw improved or updated input methods, such as switching from a cassette to a floppy disk, incorporating automatic functions for indexing, recall, and editing, or allowing for communication with other devices. Several devices, such as the Rose Reader which was projected to be a full-page, 25-line refreshable display for less than $7500 [40], never made it past a prototype phase to production.

Fig. 4
A timeline of major milestones in refreshable braille (left) and tactile graphics devices (right) *Courtesy of the Museum of the American Printing House for the Blind (Accession Number 1992.283a-b, Object ID 1995.1, and Object ID 2014.7.42) ** Courtesy of Bristol Braille Technology
Fig. 4
A timeline of major milestones in refreshable braille (left) and tactile graphics devices (right) *Courtesy of the Museum of the American Printing House for the Blind (Accession Number 1992.283a-b, Object ID 1995.1, and Object ID 2014.7.42) ** Courtesy of Bristol Braille Technology
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Table 1

A summary of significant refreshable braille and tactile graphic devices

Device NameCompanyDevice typeRelease datePriceMechanism
Optacon [26]Telesensory SystemVibrotactile Device1971$3,400Piezo-electric vibrotactile array
Braillex [38,39]PapenmeierRBD1975UnknownPiezo-electric
Elfina Digicassette [34,35]Murac MicromaticRBD1975-1977$2,600Piezo-electric
Braillocord BRS 76 [38,39]AID Electronik GmbHRBD1976$3,500Piezo-electric, 32 cells
VersaBraille [25]Telesensory SystemRBD1979UnknownPiezo-electric, 20 6-dot braille cells
BrailleNote [42]HumanWare and PulseDataRBD2000$4,795 to $5,795aPiezo-electric, 18 or 32 cells
PAC Mate Notetaker [43]Freedom ScientificRBD2003$1,428 to $8,814.75aPiezo-electric, 14 to 80 cells
Brailliant [44]HumanWareRBD2004$2,199 to $5,795aPiezo-electric, 18 to 40 cells with Bluetooth compatibility
Seika [48]Perkins School for the BlindRBD2009$2,495Unknown, 40 cell
Orbit Reader 20 [49]Orbit ResearchRBD2016$649 to $1,499aProprietary, 20 and 40 cells
Braille Me [48]InnovisionRBD∼2017$500Proprietary magnetic actuators, 20 cells
Canute [45]Braille Bristol TechnologyMulti-Line RBD2020$3,195aRotational, 9 lines of 40 cells
Orbit Slate 520 [46]Orbit ResearchMulti-Line RBD2023$3,495aProprietary, 5 lines of 20 cells
Kurzweil Reading Machine [19]Kurzweil Computer ProductsAudio Reader∼1980$22,000N/A
The Reading Edge [55]Kurzweil Computer ProductsAudio Reader1992$6,000N/A
K-NFB Readers [55]Kurzweil/National Federation of the BlindAudio Reader2005$3,495N/A
K-NFB Reader App [55]Kurzweil/National Federation of the BlindAudio Reader∼2006$100N/A
VT Touch [56,57]VirTouchGraphical Display Mouse∼2001UnknownN/A
DV-1, DV-2 [54,62,63]KGS, IncTactile Graphics Display∼1990 s$13,500 to $50,000Solenoid pins, 768 to 3072 taxel displays
VideoTIM [65]ABTIMVibrotactile Device∼2010UnknownPiezo-electric vibrotactile array
Maple-GWP [66]Handy Tech GmbH (now Help Tech)Tactile Graphic Portal2001$10,000Piezo-electric, 24 × 16 tactile portal
HyperBraille [63,71]MetecMulti-Line Tactile Device2007>$50,000aPiezo-electric tactile dipslays, 1872, 3648, and 6240 taxels
TACTS 100 [74]Tactisplay Corp.Multi-Line RBD2015$2,000aPiezo-electric, 4 lines of 25 cells
TACTIS Walk [74]Tactisplay Corp.Multi-Line Tactile Device2015$7,000aPiezo-electric sweep actuation, 3072 taxels
TACTIS Table [74]Tactisplay Corp.Multi-Line Tactile Device2015$12,200aPiezo-electric sweep actuation,12000 taxels
Graphiti [75,76]APH and Orbit ResearchTactile Graphics Display2017$25,000aProprietary, 2400 touch sensitive taxels
Device NameCompanyDevice typeRelease datePriceMechanism
Optacon [26]Telesensory SystemVibrotactile Device1971$3,400Piezo-electric vibrotactile array
Braillex [38,39]PapenmeierRBD1975UnknownPiezo-electric
Elfina Digicassette [34,35]Murac MicromaticRBD1975-1977$2,600Piezo-electric
Braillocord BRS 76 [38,39]AID Electronik GmbHRBD1976$3,500Piezo-electric, 32 cells
VersaBraille [25]Telesensory SystemRBD1979UnknownPiezo-electric, 20 6-dot braille cells
BrailleNote [42]HumanWare and PulseDataRBD2000$4,795 to $5,795aPiezo-electric, 18 or 32 cells
PAC Mate Notetaker [43]Freedom ScientificRBD2003$1,428 to $8,814.75aPiezo-electric, 14 to 80 cells
Brailliant [44]HumanWareRBD2004$2,199 to $5,795aPiezo-electric, 18 to 40 cells with Bluetooth compatibility
Seika [48]Perkins School for the BlindRBD2009$2,495Unknown, 40 cell
Orbit Reader 20 [49]Orbit ResearchRBD2016$649 to $1,499aProprietary, 20 and 40 cells
Braille Me [48]InnovisionRBD∼2017$500Proprietary magnetic actuators, 20 cells
Canute [45]Braille Bristol TechnologyMulti-Line RBD2020$3,195aRotational, 9 lines of 40 cells
Orbit Slate 520 [46]Orbit ResearchMulti-Line RBD2023$3,495aProprietary, 5 lines of 20 cells
Kurzweil Reading Machine [19]Kurzweil Computer ProductsAudio Reader∼1980$22,000N/A
The Reading Edge [55]Kurzweil Computer ProductsAudio Reader1992$6,000N/A
K-NFB Readers [55]Kurzweil/National Federation of the BlindAudio Reader2005$3,495N/A
K-NFB Reader App [55]Kurzweil/National Federation of the BlindAudio Reader∼2006$100N/A
VT Touch [56,57]VirTouchGraphical Display Mouse∼2001UnknownN/A
DV-1, DV-2 [54,62,63]KGS, IncTactile Graphics Display∼1990 s$13,500 to $50,000Solenoid pins, 768 to 3072 taxel displays
VideoTIM [65]ABTIMVibrotactile Device∼2010UnknownPiezo-electric vibrotactile array
Maple-GWP [66]Handy Tech GmbH (now Help Tech)Tactile Graphic Portal2001$10,000Piezo-electric, 24 × 16 tactile portal
HyperBraille [63,71]MetecMulti-Line Tactile Device2007>$50,000aPiezo-electric tactile dipslays, 1872, 3648, and 6240 taxels
TACTS 100 [74]Tactisplay Corp.Multi-Line RBD2015$2,000aPiezo-electric, 4 lines of 25 cells
TACTIS Walk [74]Tactisplay Corp.Multi-Line Tactile Device2015$7,000aPiezo-electric sweep actuation, 3072 taxels
TACTIS Table [74]Tactisplay Corp.Multi-Line Tactile Device2015$12,200aPiezo-electric sweep actuation,12000 taxels
Graphiti [75,76]APH and Orbit ResearchTactile Graphics Display2017$25,000aProprietary, 2400 touch sensitive taxels
a

Reflects the current market price at the time of writing.

Note: All other prices reflect the product price at release.

Since the sharp rise of refreshable braille in the 1970s and 1980s, improvements to the piezo-electric design have been minimal [41], despite many attempts at achieving a full page of refreshable braille or even just hitting an accessible price point. In 2000, BrailleNote, a notetaker with refreshable braille display was released as a collaboration of HumanWare and PulseData. Current versions have 18 or 32 cells and are $4795 and $5795, respectively [42]. In late 2003, Freedom Scientific released its PAC Mate notetaker with 20- and 40-cell versions, and their current line of refreshable braille products have 14 to 80 cells and range in price from $1428 to $8814.75 [43]. In 2004, HumanWare released the first refreshable displays with Bluetooth capability with the Brailliant line of products [44] and their current line features 18 to 40 cell displays ranging from $2199 to $5795. More recently, the Canute was released in 2020 as the world's first multiline refreshable braille [45]. It has 9 lines of 40 cells and costs $3195. Similarly, Orbit Research released the Orbit Slate 520, a multiline refreshable braille display with 5 lines of 20 cells at a price of $3495 [46].

Attempts at lower-cost refreshable braille displays include a rotary device developed by the National Institute of Standards and Technologies in 1999 that substantially reduced the number of actuators required and used passive pin displacement but never made it to production [47]. In 2009, Seika was introduced by the Perkins School for the Blind as a 40-cell lower-cost device for $2495 [48]. After accepting a challenge to produce a refreshable display that costs less than $500, Orbit Research released the Orbit Reader 20 in late 2016 [49]. There are now 20-cell and 40-cell versions available for $649 and $1499, respectively. Similarly, Innovision developed a novel, proprietary magnetic actuating technique resulting in a substantially reduced cost device with the 20-cell Braille Me display for $500 sold in the United States by the National Braille Press [50]. Still, more attempts at low-cost refreshable braille are in the production development or prototyping stages including the ReadRing, a proprietary rotary braille device that has demonstrated efficacy in young students of braille [51], and Readable, a lower-cost electromagnetically actuated single refreshable braille cell [23]. It should be noted, though, that single-cell refreshable static and dynamic braille has been previously attempted in the 90 s by multiple research labs, including Pantobraille and Braille Movie, which each encountered issues in reading performance due to lack of haptic perception [52,53].

4 Tactile Graphic Displays

Like embossed braille, embossed tactile graphics are bulky, fragile, and expensive to generate. Tactile graphic displays are a means of presenting graphical information via taxels, the tactile equivalent of a pixel of information. Tactile graphic displays can be classified as either static refreshable devices, in which an image is displayed ideally across a larger screen for a period of time and then refreshed, or dynamic devices that continually refresh upon movement. A comprehensive review of static and dynamic tactile displays can be found in Vidal-Verdú [54].

In parallel to the rise in use of the Optacon, was the rise in optical character recognition and text-to-speech synthesizers. In 1976, at a conference with the National Federation of the Blind, Ray Kurzweil debuted the Kurzweil Reading Machine, a large device that combined a flatbed scanner, omni-font optical character recognition, and a text-to-speech synthesizer to read aloud any scanned document. In the early 1980s, Kurzweil Reading Machine devices were sold for $22,000 [19]. Many iterations of this initial device were released that were smaller, more affordable, and of higher functionality, including The Reading Edge which was released in 1992 at a price of $6000 and the K-NFB reader originally released in 2005 for $3495 which is now available as an app on iOS, Android, and Windows 10 devices for $100 [55]. Optical character recognition provided a robust, though initially costly, solution to printed information access. Despite its limitations in conveying anything other than text, including graphs and equations, its advances largely outpaced those in tactile graphics devices.

Consequently, after the discontinuation of the Optacon in 1996, very few substantial advancements in commercialized tactile graphic displays occurred and most never made it to production. One that did briefly was the VT Touch by VirTouch, Inc. of Israel, which utilized their proprietary Virtual Touch System, with two 4 × 4 pin arrays mounted on the top of a computer mouse to display virtual graphics [56,57]. Several research projects have attempted to design similar devices by retrofitting an off-the-shelf mouse with a Metec braille cell [58], retrofitting an off-the-shelf mouse with KGS Corp. solenoid-driven pin and electromagnet for force feedback [59], or augmenting the VT Touch [60].

In the mideighties, Metec, a German company who pioneered refreshable braille, introduced a large static tactile display that produced graphics and/or multiline braille text using a solenoid actuated array of 7200 taxels [54,61]. In the late 1990s, KGS, Inc. of Japan also produced a large tactile display with 3072 taxels priced near $50,000, and smaller, lower cost versions, DV-1 with 768 taxels for $16000 and DV-2 with 1536 taxels priced under $13,500 [54,62,63]. Several research efforts have modified the Metec display, the smaller KGS displays, or even single cells in attempts to produce lower-cost, larger display options, but none have been commercialized at this time. Rotard et al. [61] collaborated with Metec to develop “Stuttgarter Stiftplatte,” a system that displays webpages including graphical information. The device was promising, but was large, not a stand-alone unit, and had a slow refresh rate of about 30 s. The Pantobraille used a KGS braille cell in combination with a force feedback device within a 10 × 16 cm workspace to allow interaction with a graphical interface, read braille, and identify texture and basic graphics [53]. Shimdada et al. [64] coupled four KGS SC–10 tactile graphic units and modified the display output such that it could be directly manipulated by the user for real-time graphic display interaction.

VideoTIM by ABTIM, essentially a re-engineered Optacon, was released with 256 piezo-actuated taxels [65]. Motivated by the increasing use of graphing calculators in public schools, in 2001, Handy Tech GmbH (now Help Tech) of Germany described a dynamic tactile graphics system for use in math classes called the Maple-GWP-System (GWP for Graphic Window Professional) [66]. It consisted of a 24 × 16 taxel array with piezo-electric actuators that interfaced with standard and customized software to produce tactile images as well as speech and braille output for around $10,000 [54,63,67,68]. In 2002, the National Institute of Standards and Technology published details of their refreshable tactile graphic display that utilizes passive pins with a single latching system and vector graphics [69]. It was nonexclusively licensed to Elia Life Technology in 2007, but at the time of writing, no updates can be found [70].

In 2007, Metec began working on what would be called the HyperBraille line of tactile graphics displays with 7200 taxels in a 60 × 120 touch-sensitive array now utilizing piezo-electric actuators [63,71]. Prices were well over $50,000 and Metec currently has three tactile displays, the Tactile2D with 1872 taxels in a 48 × 39 array, the Hyperflat with 3648 taxels in a 76 × 48 array, and the Hyperbraille F with 6240 taxles in a 104 × 60 taxel array [72]. Metec's line of tactile graphics represents a gray area in device distinction as they output both refreshable braille and tactile graphics. Several research efforts have utilized modified hyperbraille devices, including the STEM Accessibility System which increased the resolution of a mini-hyperbraille unit by pairing it with a mechanical XY gantry resulting in a higher resolution, lower-cost device [73].

In 2015, Tactisplay Corp. of South Korea launched the TACTIS 100, TACTIS Walk, and TACTIS Table. The TACTIS 100 has 4 lines of 25 braille cells for about $2000. TACTIS Walk has 3072 taxels in a 48 × 64 array actuated in a scanning sweep to reduce the number of actuators while still achieving a 6 s refresh rate for about $7000. Similarly, TACTIS Table has 12000 taxels in a 120 × 100 array for tactile graphics or equivalent to 100 braille cells for refreshable braille output for about $12200 [74]. In 2016, collaborators The American Printing House for the Blind and Orbit Research announced the Graphiti™ affordable tactile graphics display, with the first version to have 2400 touch-sensitive, multiheight pins in a 60 × 40 array expected to hit the market in 2017 for around $15000 [75]. It's sold today for about $25000 and has unprecedented functionality [76].

Several tactile graphic displays are in the prototyping phase, including BLITAB, Holy Braille, and the Monarch. BLITAB Technology is a GmbH company that designed BLITAB, which claims to be the world's first tablet for the blind and visually impaired. It is an Android tablet with 14 rows of 23 braille cells actuated using smart liquids at an anticipated cost of $500 [77,78]. The Holy Braille project is an effort started at the HAPTIX Lab at the University of Michigan and transitioned to NewHaptics in which microfluidic technology is utilized to control pneumatic actuators for a full page refreshable braille and tactile graphic page [20,79]. The Monarch (formerly the Dynamic Tactile Display) is being developed via a collaboration of the American Printing House for the Blind (APH), HumanWare, and the Digital Accessible Information System (DAISY) Consortium, as well as a partnership with the National Federation of the Blind [80]. It draws on increased functionality that was deemed necessary after the release of Graphiti™ and utilizes a new proprietary cell technology from Dot Incorporated. It has an educational focus to increase access to braille textbooks and tactile graphics and will have an equivalent of 10 lines of 32 braille cells. As of the time of writing, APH has not yet estimated a price but estimates the device to be on the market in late 2024 [81].

5 Biomechanical Considerations of Refreshable Braille and Tactile Graphic Design

Braille and tactile graphic discrimination necessitate the multisystem coordination of mechanotransduction, motor control movements, and cognitive-linguistic processing of the highest order [8284]. The fundamental mechanisms regulating the transfer of mechanical stimuli to the mechanoreceptors of digital skin are exceedingly complex and not yet well understood. In contrast, due in part to rapid advances in technology, the kinematics of the braille reading finger have been repeatably quantified, but not easily linked to their exact role in cognitive linguistic processing.

5.1 Skin Biomechanics of Tactile Perception.

As integral as optics and acoustics are to visual and auditory perception, skin biomechanics are essential to the understanding of tactile perception. Braille and tactile graphic discrimination is a complex, multisystem process involving the neural encoding of a spatio-temporal distribution of mechanical stimuli across contacting skin tissue in which viscoelastic deformations of the skin stimulate the primary mechanoreceptors innervating the glabrous digital skin [85]. Despite decades of psychophysiologic, neural-transduction, and biomechanics research efforts, the mechanisms and pathways of digital mechanotransduction are not fully defined [86].

There are four low threshold mechanoreceptor afferents associated with tactile perception of the digital skin with a minimum activation force reported between 5 and 2 mN [87]. They are the Meissner corpuscle (RAI), Merkel cell complex (SAI), Pacinian corpuscle (RAII), and Ruffini corpuscle (SAII), each having unique frequency ranges, force thresholds, receptive fields, and spatial density. They are classified as rapidly adapting (RA) or slowly adapting (SA) which refers to the rate of neural transduction in the presence of a static stimuli. Meissner corpuscles (RAI) and Merkel disk complexes (SAI) are located in the dermal papillae near the dermal-epidermal junction, are relatively smaller in size, have multiple peak sensitivities, and have well-defined receptive field borders [8790]. In contrast, Pacinian corpuscles (RAII) and Ruffini corpuscles (SAII) are located deep within the dermis, are relatively larger, have a single sensitivity peak, and undefined receptive field borders (Fig. 5(b)) [91].

Fig. 5
Adapted from (a) Phillips et al. [103] who first reported these foundational results in a study of the representation of braille by individual mechanoreceptor afferents, effectively demonstrating that SA I and FA I (RA I) afferents alone can discriminate braille. A set of braille cell characters (A through R in the top line) were repeatedly scanned by either the distal phalanx of the index or middle finger at a rate of 600 mm/s with an application force of 60 g. The resulting spatial events plots were created using responses of individual human mechanoreceptor afferents, including Merkel disks (SA I), Meissner corpuscles (FA I), Ruffini endings (SA II), and Pacinian corpuscles (FA II). The braille cell characters are distinctly visible in the spatial event plots reconstructed for the SA I and FA I (RA I) afferents. Used with permission from Ref. [103]. (b) The relative location of the four primary mechanoreceptors of glabrous digital skin are depicted near the boundary of the dermal-epidermal junction and their receptive properties are summarized [87,93,94]. For comparison, the mechanoreceptors are matched to the spatial events plot in (a).
Fig. 5
Adapted from (a) Phillips et al. [103] who first reported these foundational results in a study of the representation of braille by individual mechanoreceptor afferents, effectively demonstrating that SA I and FA I (RA I) afferents alone can discriminate braille. A set of braille cell characters (A through R in the top line) were repeatedly scanned by either the distal phalanx of the index or middle finger at a rate of 600 mm/s with an application force of 60 g. The resulting spatial events plots were created using responses of individual human mechanoreceptor afferents, including Merkel disks (SA I), Meissner corpuscles (FA I), Ruffini endings (SA II), and Pacinian corpuscles (FA II). The braille cell characters are distinctly visible in the spatial event plots reconstructed for the SA I and FA I (RA I) afferents. Used with permission from Ref. [103]. (b) The relative location of the four primary mechanoreceptors of glabrous digital skin are depicted near the boundary of the dermal-epidermal junction and their receptive properties are summarized [87,93,94]. For comparison, the mechanoreceptors are matched to the spatial events plot in (a).
Close modal

Meissner corpuscles (RAI) are located at the apex of dermal papillae in the dermal-epidermal junction and are therefore the most superficial mechanoreceptor afferent. They have the highest spatial density at approximately 141 units/cm2 and are responsive to extremely low magnitude, low-frequency forces within a 40–60 Hz range [86,92]. Merkel disk complexes (SAI) are located along the rete ridges at the dermal-epidermal junction with an approximate density of 70 Merkel cells/cm2 [92]. They have a high spatial resolution acuity, a frequency range below 10 Hz, and variable, but defined receptive field [93]. Merkel disk complexes are sensitive to static pressure and shear stress caused by points, edges, and spatial features such as form and texture [86,87].

Pacinian corpuscles (RAII) are relatively large 1 mm cells located deep within the dermal layer with a spatial density of approximately 21 units/cm2 [91,92]. Extraordinarily frequency dependent, Pacinian corpuscles operate as a robust low pass filter, sensitive to high frequency, low magnitude forces resulting from as small as nanometer-scale deformations [86]. They are sensitive to frequencies as high as 500–600 Hz and reach optimal sensitivity around 200 Hz. Pacinian corpuscle receptive fields are not well defined but are expansive and have been shown to detect distant events via vibration through objects, such as hand tools [86,87,94]. Ruffini corpuscles (SAII) are also located deep within the dermal layer with the lowest reported spatial resolution of 9 units/cm2 [92]. Conflicting evidence surrounds Ruffini corpuscles, but it is hypothesized that they are responsible for the perception of global hand positioning via skin stretch and deviatoric stress activation [86].

5.2 Digital Mechanotransduction and Implications For Design Specifications.

The distinct properties of the mechanoreceptor afferents, specifically the optimal frequency sensitivity, perceptive ability, and receptive field, can be utilized to optimize the design of refreshable braille and tactile graphics devices. It is unsurprising that, given that the Optacon was groundbreaking in its ability to successfully convey tactile information to the blind and low-vision community, that it was widely utilized in psychophysical studies of afferent nerves shortly after its release [95101]. Gardner and Palmer [102], found that the Optacon activated the Meissner (RAI) and Pacinian (RAII) afferents, but not the Merkel disks (SAI) or Ruffini corpuscles (SAII). These results suggested an explanation for reduced reading performance of the Optacon, as Pacinian afferents have a distinct low spatial resolution. As such, these results were critical to the reinforcement of the hypothesis of the role of RAI and RAII afferents in the detection of global motion, as the Optacon is extremely effective at conveying motion and changes in motion [101].

The mechanoreceptors associated with effective braille and tactile graphic discrimination are debated, though it is often hypothesized that it is not a single mechanoreceptor, but a complementary combination of rapidly and slowly adaptive afferents. Gardner and Palmer [102] demonstrated that the rapidly adapting afferents alone cannot localize a stimulus due to a lack of spatial acuity and hypothesized that localization occurs via a combination of Meissner corpuscles (RAI), Merkel disk complexes (SAI), and Pacinian corpuscles (RAII). Phillips et al. [103] in an elegant study, demonstrated that Meissner corpuscles (RAI) and Merkel cell complexes (SAI), robustly and independently resolved braille dot characters, whereas Pacinian corpuscles (RAII) and Ruffini corpuscles (SAII) were unable to alone (Fig. 5(a)). Taken together with the results of previous Optacon studies, Phillips et al. hypothesized that it is the combination of RAI and SAI that effectively resolves braille characters and allows braille to overcome the inherent low pass filters of the skin. In a later study of scanned embossed dots, Phillips et al. [104] investigated the spatial acuity of both rapidly and slowly adapting afferents demonstrating that RAI and SAI resolved dots as close as 1.5 mm and RAII and SAII resolved dots as close as 3.5 mm. Given the prescribed spacing of braille characters, this reinforces previous hypotheses of the role of RAI and SAI in braille discrimination. Masic et al. [105] hypothesizes that RAI and RAII are crucial for braille discrimination due to their ability to provide sequential global positioning information, a mechanism that is imperative for braille scanning and may be a reason why static, single-cell braille discrimination is more difficult. Johnson et al. [106] described the complementary nature of SAI (low sensitivity, high resolution) and RAI (high sensitivity, low resolution) mechanoreceptors in tactile discrimination as analogous to rod and cone cells in optical discrimination. Future efforts should investigate further the intricate mechanoreceptor combinations relevant to braille and tactile graphic discrimination tasks.

Taken together, this information informs the design specifications of refreshable braille and tactile graphic devices as the tactile properties of each mechanoreceptor can be exploited for device optimization, specifically the distinct spatial and temporal differences between receptors. Tactile acuity has been demonstrated to be exceptional, allowing for the detection of textural differences as small as 10 nanometers [107] and surface features, such as a dot on a flat surface, as small as 1 to 3 microns in height and 550 microns in diameter [108,109]. Despite blind persons having a fingertip spatial threshold range of about 1.0 to 1.5 millimeters (about 15% higher tactile acuity than sighted peers) [110], refreshable braille and tactile graphics devices have generally maintained the standard of pin height and spacing standards set by the Braille Authority of North America (BANA). These require that the pin diameter is 1.5–1.6 mm, the distance between two pins in the same cell is 2.3–2.5 mm, the distance between corresponding pins in adjacent cells is 6.1–7.6 mm, the pin height is 0.6–0.9 mm, and the distance between corresponding pins from one cell above or below is 10.0–10.2 mm [111]. These specifications are well below the spatial acuity of fingertip mechanoreceptors. This is especially notable given that the superior tactile spatial acuity of those in the blind and low vision community has been demonstrated in multiple studies [110,112116] as well as the ability to recruit the visual cortex for additional somatosensory processing [112,117,118]. Lei [119] demonstrated that pin heights of 0.18 mm and 0.38 mm did not cause reading regressions of speed or regressive movements. This is an important result given that BANA standards are 0.6–0.9 mm, as a reduction of pin height requirements, and consequently, actuator linear stroke lengths could allow for more successful implementations of alternative actuators.

A limited number of devices have been developed utilizing the distinct properties of mechanoreceptors as explicit design constraints. Much like the Optacon, these efforts often focus on vibrotactile stimulation by targeting optimal frequency ranges of a single mechanoreceptor, while others utilize direct electrical stimulation. Zhao et al. [120] designed a vibrotactile conventional braille display that exploited the Meissner corpuscle, Pacinian corpuscle, and Ruffini ending properties by using shape memory alloy to vibrate within the optimal mechanoreceptor ranges, with peak participant performance at 50 Hz. Puertas et al. [121] developed a braille display that applied direct electrical stimulation via voltage simulating the pressure and deformation of equivalent embossed braille, causing less discomfort than current-delivered counterparts. Carpi et al. [122] proposed a portable, low-cost refreshable braille device utilizing hydrostatically coupled dielectric elastomer actuators operating within the optimal frequency range of Pacinian corpuscles, which they defined as 250–300 Hz.

5.3 Computational Modeling of Mechanotransduction.

Defining the properties of mechanoreceptors is deeply dependent on the ability to accurately describe the deformations that they are subject to across varying stimuli. The transfer of cutaneous stimuli through the intricate and site-dependent layers of the epidermal and dermal tissues, let alone the complex cell bodies of mechanoreceptors, is not well studied despite decades of mechanoreceptor research [87]. A growing body of research efforts is utilizing multiscale computational modeling to elucidate the transfer of mechanical stimuli to deformations of individual mechanoreceptors (Fig. 6(b)). Dandekar et al. [123] developed and parametrically calibrated a multilayer model of both a macaque monkey and a human finger demonstrating the need to incorporate multiple tissue layers in tactile models. Additionally, the model results reinforced previous observations that SAI afferents are sensitive to the global shape of an object. Gerling and Thomas [124] utilized finite element modeling to study Merkel disk (SAI) sensitivity to the gap axis of an indentor, the significance of which is that Merkel disks are hypothesized to discriminate edges. The model demonstrated that a gap axis parallel to papillary ridge lines resulted in higher transmitted stresses, potentially informing the optimal orientation of tactile stimuli. Vodlak et al. [125] developed a novel multiscale model of the Meissner corpuscle that coupled tissue-level and cell-level structural mechanics models with a two-stage electrophysiologic model and validated results with experimental neurographic data. Quindlen et al. [126] in a multiphysics computational model of the Pacinian corpuscle that included outer and inner biomechanics as well as neurite electrochemsity due to a vibratory input, demonstrated that the stimulus was amplified by a factor of 8–12 within the Pacinian structure. Maeno et al. [127] constructed a finite element model of the finger that demonstrated the dependence of individuals rapidly and slowly adapting mechanoreceptor stress/strain states on the shape of the papillary ridges. Similarly, Shao et al. [128] implemented a two-dimensional, multilayer model of sliding contact between a finger and textured surfaces to elucidate the effects of papillary ridges on the stress variations that subsequently activate Meissner (RAI) and Pacinian (RAII) corpuscles. The model demonstrated that papillary ridges have minimal effects in static loading conditions, but significantly increase oscillations during sliding. Jobanputra et al. [129] investigated the effects of age-related skin changes on tactile perception by developing a hyperelastic, four-layer model simulating a finger sliding across a rigid surface and the resulting strain, deviatoric stress, and strain energy densities at Meissner corpuscle and Merkel disk complexes. Changes in skin stiffness, flattening of the dermal papillae at the dermal-epidermal junction, and dermal thinning all contributed to a reduction in stimuli magnitudes at the mechanoreceptor level. Overall, computational models have focused more on multiphysics models to include neural-transduction pathways and sliding contact between textured surfaces in the context of papillary ridge involvement.

Fig. 6
The forces imparted by the braille pin on the braille reading finger (a) are transferred through the complex layers of the skin to the various mechanotransducers. The inherent complexity of skin tissue makes characterizing this force transfer extremely difficult. Adapted from Jobanputra [129], computational models (b) are currently utilized to determine how forces transfer from the superficial tissue to the deeper layers where the various mechanotransducers are located. Created with Bio-Render.com.
Fig. 6
The forces imparted by the braille pin on the braille reading finger (a) are transferred through the complex layers of the skin to the various mechanotransducers. The inherent complexity of skin tissue makes characterizing this force transfer extremely difficult. Adapted from Jobanputra [129], computational models (b) are currently utilized to determine how forces transfer from the superficial tissue to the deeper layers where the various mechanotransducers are located. Created with Bio-Render.com.
Close modal

Similar to the multiscale models of Vodlak and Jobanputra, future finite element analyses should utilize multiscale modeling techniques to elucidate the transfer of stimuli throughout the complex epidermal and dermal layers, especially in locations of individual mechanoreceptors and even within the mechanoreceptor cell bodies themselves. Furthermore, these multiscale models need refined input data within the context of braille and tactile graphic perception. Watanabe et al. [130] measured the normal contact force during braille reading, ranging from 0.4 N at the beginning to 1.2 N after 45 s of reading, but these data were limited by the dependence on point of contact and the differing methods of braille reading utilized by study participants. Saadeh and Trabia [131] developed a system to measure and characterize normal and tangential fingertip forces in braille reading, resulting in a normal force of 0.426 ± 0.262N and a lateral force of 0.420 ± 0.205N. It is important to note that each of the study participants were adults. The forces generated by early braille literacy students could be significantly different, effecting the activation of the light touch afferent system characteristic of braille perception (Fig. 6(a)). Experimental characterization of these forces will provide valuable input for computational models such that costly design iterations can be completed via simulation prior to prototyping. Furthermore, computational modeling may be used to optimize braille spatial dimensions or even guide the development of direct stimulation modalities.

5.4 Motor Control Development and the Kinematics of the Braille Reading Finger.

The process of tactile discrimination inherently requires well-developed gross and fine motor control of the arm and hand [132]. Motor delays have been consistently identified within the blind and low-vision population [132138]. These motor delays manifest as early as infancy, through self-initiated mobility, locomotion, and fine motor delays, with the most significant delays occurring in preterm groups [133,135]. Troster and Brambring [135] demonstrated in a study of congenitally blind and sighted infants that the blind infants experienced delays in both areas directly affected by vision loss (locomotion and fine motor) as well as those that are not (posture control). Subsequent studies of motor control in blind and low vision infants and children confirmed that the delays are caused primarily by a lack of visual stimulation and secondarily by a lack of motor stimulation, social interaction, and even cognitive prerequisites, such as object permanence via auditory feedback [133135,138,139]. Levtzion-Korach et al. [138] emphasized that the motor development delays experienced by blind and low-vision children could be shortened by access to appropriately stimulating environment. This environment may be found in the home from the parents, outside the home via an orientation and mobility specialist, or in a school setting [140142]. Interestingly, Aki et al. [142] demonstrated that an out-of-home training program was significantly more effective than an in-home program, emphasizing the need for targeted and intentional rehabilitation. Motor development in the blind and low-vision population is imperative, as the distinct kinematic movements of the braille reading finger have been attributed primarily to limb motor control and psycholinguistic factors [83].

Just as eye tracking can be used to track the reading performance of sighted readers, movement tracing of the braille reading finger(s) can be used to understand the development of braille reading skills or evaluate performance. Early studies of braille reading movements were observational and determined that proficient braille readers utilized a smooth sweeping motion across a line of braille, whereas less proficient readers exhibited irregular scrubbing movements as text was deciphered [143]. Davidson et al. [144] were the first to attempt to quantify braille reading movements in eighteen adolescents by using video recordings of the tops and bottoms of hands during reading tasks. The key results were foundational in the understanding of braille reading movement, including the consistency of a particular style and positioning of hands throughout reading, which is thought to reduce haptic noise, and the use of regressive movements, a characteristic common in less proficient readers. Building on these efforts, Hislop et al. [145] were the first to compare Optacon reading performance (using both letter print and braille print) to conventional braille by recording finger traces using the instantaneous position of an LED mounted either on the fingertip or the Optacon camera. No significant differences in reading movement patterns were found between the three modes explored, despite the Optacon letterprint having a lower reading rate (25.2 adjusted words per minute) than the embossed braille reading rate (106.8 words per minute). As in previous studies, less proficient readers were shown to make more frequent regressions.

Hughes et al. [83] investigated the causes of velocity intermittencies of the reading finger by continuously recording finger position with a digitizing tablet and pen fitted to the subject's fingertip. The resulting velocity range for a single dominant reading finger was 1–10 cm per second with a mean of 3 cm per second with no smooth or constant motion, a characteristic that the authors suggest is likely primarily due to slow movement motor control, as well as psycholinguistic and haptic exploratory factors. This intermittency is not thought to be isolated to braille discrimination due to the phenomenon existing in nonhaptic-related tasks [146148]. In a similar study of braille reading fingertip position, Wei et al. [84] studied the ability to discriminate changes in cell numerosity and changes in cell arrangement and the accompanying motor control of exploratory movements. The results demonstrated that slower finger movements resulting in higher numerosity perceptual performance always experience more velocity intermittency than faster movements.

Most recently, Nonaka et al. [149] in one of the only longitudinal studies of braille kinematics in children, investigated whether the quantitative kinematics of the braille reading finger related to overall braille reading performance. The study focused on two aspects that had not yet been evaluated, the temporal correlations of velocity variation and the variability in the orientation of the fingerpad to the braille dots. The results demonstrated correlation between the strength of long-range temporal correlations in lateral scanning movements to braille reading performance, and notably, an inverse relationship between variations in orientation of the reading finger and braille reading performance. This result alone has far-reaching implications for the design specifications of refreshable braille and tactile graphics, as they demonstrate that fine adjustment exploratory movements of high-resolution receptor surfaces enable efficient tactile discrimination, effectively narrowing the field dimensions of the tactile elements. It should be noted that the majority of these studies were performed on subjects with no significant comorbidities that may have affected their ability to read braille text. In the broader population, however, that number is approximately 40% [150]. Additionally, Brambring [134] found variability in gross motor skills across a group of blind and visually impaired children. Taken together, these data imply that future refreshable braille and tactile displays will require easily customized features to accommodate differences such as atypical hand or arm positioning and limited range of motion. Future work will necessarily require kinematic analyses that can be performed quickly and used to inform subject-specific modifications to the device.

6 Actuator Technology

During the development of the Optacon, tactile graphics and haptics research were initially and primarily motivated by the need to create novel haptic interfaces for astronauts and pilots. Funding first from NASA and the Department of Defense, and only later from the Department of Education, largely enabled its successful development [151]. Similarly today, heightened interest in virtual reality, robotic surgery, telesurgery, and various military applications has led to a sharp increase in broad haptics funding opportunities [152154]. The resulting research has focused heavily on novel actuator technologies.

There are many former and ongoing research efforts that address the advancement of actuators. Yang et al. [155] provide a comprehensive survey on the state of the art of actuator advancements in the context of refreshable braille devices and tactile graphics displays. Briefly, actuator options that have been investigated are pneumatic, hydraulic (microfluidic), electromagnetic, micro-electromechanical systems, electrorheological fluids, magnetorheological fluids, bimetallic thermal expansion actuators, shape memory alloys, electro-active polymers, and piezo-electric actuators (including piezovibrotactile actuators), each with their own set of tradeoffs [41,155157]. Those tradeoffs include actuator cost, response time, blocking force, power requirements, stroke length, hysteresis, and reliability. Vidal-Verdú and Hafez [54] summarize the actuation method used by numerous static and dynamic tactile displays. More recently, except for the rotary braille of the Canute device, refreshable braille devices currently on the market utilize piezo-electric actuation. Similarly, the hyperbraille line of tactile graphic displays by Metec utilizes piezo-electric actuators and the Orbit Research Graphiti device utilizes proprietary technology, while the NewHaptics Holy Braille and the APH Monarch propose to use microfluidics actuation and a novel proprietary actuation, respectively.

Essential to the operation of several actuator technologies are latching structures. Latching structures are designed to hold braille pins in an actuated position against the input force of the user such that the power consumption of the actuator is limited only to the initial actuation. These include magnetic and shape memory polymer semilatching polymers and flipping or lateral moving components for full-latching structures, as described by Yang et al. [155]. Latching structures often decrease the power consumption, but concomitantly decrease the spatial resolution or contribute to overall device bulkiness due to increased cell components [154]. Despite incremental advancements in actuator and latching technology, piezo-electric actuators remain the preferred mechanism.

7 Discussion

Refreshable braille and tactile graphic displays have been a complex engineering challenge since their initial conception in the early 1970s [20,151]. Despite over fifty years of design attempts and investment from both federal and private entities, a high-fidelity, low-cost solution has yet to be developed. This is especially concerning given the rapid adoption of graphical user interfaces for human-computer interaction. Accessible technology for the blind and low-vision community has simply not kept up the pace. Various attempts from the highest levels of research and development in academia and industry described in this paper have resulted in devices that have failed to meet the needs of the end-user, typically due to a device that is extremely cost prohibitive, lacks robustness, longevity, or functionality, or is unscalable for sustainable manufacturing. Ultimately, when success is defined as increased end-user uptake, efforts at refreshable braille technology and tactile graphic displays have not yet been successful.

Central to the complexity of this design challenge is cost. The exorbitant cost ranging from $500 for a basic device (Innovision Braille Me) to a staggering $56000+ for a high-fidelity tactile display (Metec HyperBraille), puts this technology out of reach for many if not most blind and low vision braille and tactile graphic individual consumers, as well as educational systems. Efforts at cost reduction focus on either the reduction of braille cells or taxels or by attempting to design novel actuators, latching technologies, or overall display types. Reduction in cells is typically attempted by means of single-cell refreshable braille or a reduced pin graphic display that utilizes a tactile portal. Single-cell refreshable braille prevents users from using a standard two-handed butterfly technique for reading [158,159]. Similarly, tactile portals are promising such as in the Handy Tech GWP system or the VT Touch mouse, but the tactile portal only displays a small window of the global information – effectively removing or reducing the ability for whole hand and lateral exploration, exploratory procedures that are imperative for tactile graphic synthesis [63]. Several novel and emerging actuator technologies and latching structures have been explored as described above, but none of the current alternative options have significantly improved upon the piezo-electric actuator in refresh rate, blocking force, stoke length, or power requirement. Moreover, new approaches to refreshable braille and tactile graphics have explored alternative modalities that are ineffective or misguided by a lack of end-user input [160]. As such, engineering innovations are needed specifically in the development of low-cost actuators and latching systems that perform as well as their expensive piezo-electric counterparts. Similarly, further research at the intersection of mechanotransduction and braille perception is necessary to determine if alternative methods, such as direct stimulation, are viable options. As a design problem, this challenge is best approached with extensive involvement from end-users such that introduction of a new technology or modality does not reduce the fidelity or uptake of the system.

A substantive disconnect exists between emerging technologies and the specific needs of the blind and low-vision community [63,71]. Lopez et al. [161] found that when braille educators and braille users independently ranked braille technologies, the devices ranked highly by educators were ranked low by end-users. Especially given the well-established benefits of early intervention, the gap, or silo, between engineers and end-users should be closed such that a low-cost, high-fidelity device can be realized [137]. We have shown that there are distinctly different fields with unique challenges to overcome in developing refreshable braille and tactile graphics devices. A device should not be designed without carefully considering the basic mechanoreceptor properties of the skin, the motor control movements that they originate from, and the cognitive linguistic processing that results.

Convergence research approaches have received extensive recognition among scientists for the ability to address critical and complex societal challenges by integrating contributions from fields outside of life, physical, engineering, and medical sciences. The resulting teams are of the highest interdisciplinarity and diversity, both in functionality and identity, and develop exceptionally innovative and creative solutions [162,163]. The disability community has long recognized the importance of convergence through the disability rights movement mantra, “Nothing about us, without us” [164,165]. Often used in the context of policymaking, the concept extends to the design of emerging assistive technologies, including refreshable braille and tactile graphics [166]. Implementing convergence design and end-user involvement leads to reduction in design iterations due to early detection of flaws, improved device adoption, and overall consumer satisfaction [167,168]. Several devices in development (e.g., APH's Monarch and NewHaptics' Holy Braille) have included end-users in their design extensively. Many other projects have limited end-user involvement. This is often because many assistive technologies in the haptics realm are fallout technologies, meaning they have been designed for a completely different application and repurposed without context [54,169]. The inclusion of end-users needs to be done meaningfully, systematically, and prolifically, such that diversity in age, socioeconomic status, education, employment, use modality, and many more cofactors, are captured.

A repeated theme throughout the history of refreshable braille and tactile graphic design (and assistive technology in general) is the cyclic process of intensive research and design, prototype development, production, and then abandonment, usually due to lack of profit margins. Examples of this are the Optacon, the Maple-GWP-System, the VT Touch mouse, and the KGS Dots View (DV-1 and DV-2) line of products. There are far more examples of research endeavors that have been abandoned before translating into a production prototype, several of which are described above. An early example of this is the Rose Reader, which did have an initial production model but couldn't secure funding. It is important to note that barring a drastic change in actuator technology, no incremental improvement to refreshable braille and tactile graphics will change the profit margins of the resulting device. So how can the issue of cost be meaningfully addressed? In 1973, John Linvill, the inventor of the Optacon, said it best: “Government, university, and industry are symbiotic in attacking blindness with technology” [151]. One such way that Linvill advocates is federally funding the research and development through a university such that industry does not have to factor in recouping those costs in the sale price. Furthermore, Linvill emphasizes that investing in these devices is an investment in human capital which is made more productive with access to the resulting accessible technology.

Finally, refreshable braille and tactile graphics device design should consider features required for early braille literacy education to improve outcomes. It has been demonstrated that the early literacy needs for blind and low vision children are analogous to age-matched sighted children [170,171]. Steinman et al. [172] proposes that braille learners progress through a similar Chall's stage model of literacy development as print learners. Ultimately, a child who utilizes braille should be exposed to equivalent early literacy education at the same time and pace as their sighted peers. Argyropoulos et al. [173] documented that braille was a preferred reading medium of primary and secondary students, but despite this preference, students primarily chose audio readers, suggesting a gap in literacy skills, technology access, and adoption, or access to experienced braille instructors. While refreshable braille adoption and abandonment rates are not well documented, overall assistive technology abandonment rates are estimated as 30% from a survey of adults between the ages of 18 and 45 [174]. It is hypothesized that an early literacy education program that provides equitable access to high-performing refreshable braille designed within the context of the specific needs of early learners has the potential to dramatically improve device adoption rates. For young children, this includes designing pediatric-sized devices, such as the APH BrailleBuzz [175], and anticipating frequent device damage or loss, in which case developing an extremely low-cost, durable, device is especially important.

8 Conclusions and Future Directions

This paper provides a review of refreshable braille and tactile graphics focusing on technology milestones and limitations throughout the extensive design history. The path to low-cost, high-fidelity refreshable devices began in 1916 with the first patent application for a spring-loaded refreshable braille reader device. Since then, many devices have been conceptualized and commercialized. Many more devices have been prototyped and abandoned. Cost is the primary factor affecting the success of any single high-performing refreshable braille and tactile graphics device. The price is largely dependent upon the number of braille cells or taxels and the type of actuator utilized. Despite exploring many alternative actuators, the primary modality of actuation has remained piezo-electric since the vibrotactile implementation of piezo-electric bimorphs by the Optacon in 1971 and the piezo-electric actuators of the Braillex in 1975. Incremental improvements to such devices will not substantially affect the final price. Motor control kinematics and digital mechanoreceptor afferent properties are limiting factors in the success of a given device. There is little consensus on the role of various mechanoreceptors in braille and tactile graphic discrimination. Early computational modeling of the translation of stimuli through the complex layers of the skin and cell bodies shows promising results for further modeling efforts and their potential contribution to the understanding of digital mechanotransduction.

Future design attempts and refinements should place a strong emphasis on end-user involvement through a convergence design approach, thereby defining the design space based on both what the end-user deems as imperative functionality and what the technology can reasonably provide. A systematic approach to the understanding of early refreshable braille literacy exposure as it relates to refreshable braille device design specifications and subsequent longitudinal device adoption and abandonment rates is necessary. Finally, special consideration should be given to designing easily customizable or modifiable devices that meet the needs of the variable motor control skills across the blind and low-vision population. These considerations will ultimately contribute to equitable access to refreshable braille and tactile graphics.

Acknowledgment

The authors would like to acknowledge the staff at Clovernook Center for the Blind and Visually Impaired for technical advising regarding braille print and tactile graphic display technology as well as providing insight into the early braille literacy education.

Data Availability Statement

No data, models, or code were generated or used for this paper.

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