Abstract
Access solutions may facilitate communication in children with limited functional speech and motor control. This study reviews current trends in access solution development for children with cerebral palsy, with particular emphasis on the access technology that harnesses a control signal from the user (eg, movement or physiological change) and the output device (eg, augmentative and alternative communication system) whose behavior is modulated by the user’s control signal. Access technologies have advanced from simple mechanical switches to machine vision (eg, eye-gaze trackers), inertial sensing, and emerging physiological interfaces that require minimal physical effort. Similarly, output devices have evolved from bulky, dedicated hardware with limited configurability, to platform-agnostic, highly personalized mobile applications. Emerging case studies encourage the consideration of access technology for all nonverbal children with cerebral palsy with at least nascent contingency awareness. However, establishing robust evidence of the effectiveness of the aforementioned advances will require more expansive studies.
It is estimated that 40% of children with cerebral palsy, particularly those at Gross Motor Function Classification System level IV or V, experience some degree of difficulty with expressive communication. 1 Communication restrictions have been associated with delayed language development 2 and reduction in peer interactions, self-esteem, and quality of life. 1,3 Consequently, children, parents, and health care providers have identified communication enhancement as a high-priority therapy goal in cerebral palsy. 1,3,4 Indeed, functional communication fosters independence, reveals a child’s true developmental status, and allows a child to be involved in his or her care. 5
Children with cerebral palsy who have complex communication needs can benefit from access solutions that provide alternative means of communication. As shown in Figure 1, a communication access solution has 3 components—the access pathway, a signal processing unit, and the augmentative and alternative communication system. 3,6 The access pathway refers to the input used to control the system, which traditionally might be direct (eg, touching the augmentative and alternative communication device’s screen to select the object of interest) or indirect (eg, waiting for an on-screen keyboard to scan to the desired letter and then contacting one or more mechanical switches external to the augmentative and alternative communication device to make a selection). The former is user-paced whereas the latter is system-paced. The signal processing unit embodies an algorithm that processes the user input. Collectively, the access pathway and signal processing unit constitute the access technology. 6 The augmentative and alternative communication system refers to the user interface, which can be grouped into one of 3 categories: low, mid, and high-tech. Low-tech augmentative and alternative communication systems include nonelectronic devices such as printed communication boards. Mid-tech augmentative and alternative communication systems include electronic devices with a single static display and/or a scanning system with one level of choice. Finally, high-tech augmentative and alternative communication systems have dynamic displays and/or several layers of choices. 3
Schematic of a communication access solution. The access technology consists of an access pathway and signal processing unit.
Early introduction of access solutions for children with cerebral palsy can enable communication and promote the development of spoken language. 7 Sevcik and colleagues 8(p1328) proposed that access solutions should be a “first line of intervention” that can “set the stage for further language and communication development” for young children with communication difficulties.
Nonverbal children with cerebral palsy can interact with their communication partners by using gestures or vocalizations. These forms of communication require some degree of motor control on the part of the child. On the other hand, interpretation of such communicative attempts requires that the communication partner possess a high degree of familiarity with the child, including his or her behavioral idiosyncrasies, movement patterns, 9 personal preferences, 10 and daily routine. Successful communication also necessitates close attention to subtle physical cues, such as changes in the child’s body posture, eye gaze, facial expressions, vocalizations, and muscle tone. Clearly, such stringent prerequisites limit the potential number of functional communication partners for the child, as each partner must be intimately attuned to the child’s temperament and all the aforementioned behaviors. Access technologies remove some of this dependence on communication partners, allowing children to independently control augmentative and alternative communication devices and thereby develop communication abilities in a variety of social environments. 10,11
This article presents a scoping review of the current trends in access solutions for children with cerebral palsy, based on both scientific and gray literature, and the implications for clinical practice. We present the search methods, search results arranged by access technology and augmentative and alternative communication device, and a brief discussion, including emergent research.
Methods
Using the keywords cerebral palsy, communication, technology, and children (synonyms and variations thereof), we searched the following databases: Web of Science, Google Scholar, Scopus, ProQuest, and Compendex databases, for journal articles published between 2008 and October 2013. The search yielded 61 candidate articles. This list was further filtered down to 20 articles that deployed a technology-based communication solution, relating to the production of speech or text, for at least 1 young person (18 years of age or younger) with cerebral palsy. In addition, we also combed the gray literature by initially searching ProQuest with the terms communication, technology, and augmentative and alternative communication in all search fields. All information sources (blogs, podcasts, trade journals, magazines, conference proceedings, etc) except dissertations and theses were included. The search yielded 3921 items, which were then screened for relevancy to the topic area (ie, augmentative and alternative communication technology for children with cerebral palsy), yielding 37 different access solutions. For those that involved products and apps that had been released since 2008, we further visited the manufacturer or vendor websites as available to collect additional information.
Results
Our scan of the scientific and gray literature identified a changing landscape in terms of both access technologies and augmentative and alternative communication devices. The key findings will be presented under these 2 main categories below.
Access Technologies
Over the past several decades, the proliferation of consumer electronics has enabled many new means of communication for children with cerebral palsy who are nonverbal, which roughly constitutes a quarter of the pediatric cerebral palsy population. 12 For those with some controlled movement, standard (eg, trackballs, joysticks, mice, and keyboards) or adapted (eg, mechanical switches) input devices can facilitate access to communication via specialized augmentative and alternative communication hardware (Table 1) or augmentative and alternative communication software applications (Table 2) on generic computing platforms. For those capable of deictic gestures (eg, pointing), capacitive and resistive touch screen technologies offer direct access to communication devices and applications (eg, Noren et al 9 ). Likewise, individuals who can control intraoral air pressure (eg, via buccinator muscles and diaphragm) may be able to operate a “sip and puff” switch. These motor-based access methods can be effective when they cater to the specific capabilities of an individual with cerebral palsy. 45 –49 However, for many children with cerebral palsy, these access technologies are not plausible because of difficulties with switch targeting, mounting and positioning, activation with kinetic sufficiency, and release following activation. 50
High-Tech Augmentative and Alternative Communication Devices Currently on the Market (Released Since 2008).
Commercially Available Augmentative and Alternative Communication Apps Released Since 2008.
Inertial, Computer Vision, and Physiological Access Pathways
With the emergence of light weight, cost-effective sensors, advances in mobile computing hardware and new developments in pattern recognition software, individualized access technologies incorporating custom-placed sensors and personalized signal processing have become increasingly prominent in scientific literature. Table 3 provides an overview of some recent literature on state-of-the art access technologies that have been tested with modest samples of children with cerebral palsy. These technologies include video and thermal cameras that can detect and interpret limb movements, head motion and facial expressions; pressure sensors that detect switch depression with individual-specific sensitivity; magnetometers, gyroscopes, and accelerometers that sense position, angular velocity, and vibration for the purpose of detecting limb movement and vocalizations; and eye-gaze trackers that enable cursor control and icon selection. Some of these technologies are now commercially available. For example, many augmentative and alternative communication companies now offer eye gaze as an alternative access method, with the possibility of interfacing to a tablet computer. 33,51
Recent Studies Investigating Access Technologies for Children With Cerebral Palsy.
Enabling Passive Communication
In addition to active communication, where the user explicitly attempts to express himself or herself, access technologies are also being developed for passive communication. For the subset of nonverbal children who may not be able to initiate communication or respond to questions using an access pathway (ie, typically those for whom contingency awareness remains ambiguous), it is believed that enabling passive communication, that is, the automatic decoding of affective state, response to environmental stimuli, and/or personal preference may enhance their quality of care and ultimately quality of life. 52 Such information could inform the interaction with these children, including the choice of therapeutic activities, toys, and food. For this goal, researchers have investigated the usage of video cameras and various physiological sensors to track changes in skin temperature, heart activity, electrodermal activity, respiration, and facial expressions in response to certain stimuli and environmental contexts. 53 –55 Accelerometry has also been exploited for the automatic decoding of preferences of nonverbal children with hyperkinetic movements. 56 Although the above-cited studies present some promising early case evidence, the general effectiveness of these passive access modalities remains to be proven. A fundamental challenge in establishing effectiveness is the absence of ground truth; that is, these children and youth cannot confirm the verity of the inferred state or response, and often a subjective proxy validation (eg, parent or familiar caregiver) is all that is available. The fallibility of such proxy validations is highlighted by a recent study that unveiled potential inconsistencies between parental interpretation of the behavioral manifestations of preference of a nonverbal, contingently unaware adolescent with cerebral palsy, and quantitative measures of his autonomic responses. 57
Outstanding Challenges
Although the number of available access technologies has increased, evidence of their clinical effectiveness is, for the most part, only emerging. Most studies in the scientific literature have either been case studies or have, often for pragmatic reasons, tested a very small sample of pediatric participants with cerebral palsy. Nonetheless, studies to date have shown, on a small sample basis, that advanced access technologies have the ability to reduce physical exertion, increase communication efficiency, and increase accuracy over that achievable with existing input methods (eg, Falk 44 ). However, recently proposed access technologies are not immune to accidental activation by involuntary movements (eg, primitive reflexes) or voluntary movements that are not intended to control the access solution. 45 A classic depiction of this dilemma is the so-called Midas Touch predicament, in which a targeted access site bears both a technology-control intention (eg, eye gaze to move cursor) and a no-tech expressive communication function (eg, vertical eye movements to express yes or no to a communication partner). These false activations are of particular concern because of their tendency to cause unpredictable behavior in the access solution, potentially leading to frustration, learned helplessness, and abandonment. 58 It is difficult to compare accuracies of various access technologies across case studies, as they are largely dependent on the abilities of the participant, the appropriateness of the prescribed access technology for the individual, and the magnitude and quality of training provided to the user and his or her communication partners. 11
Augmentative and Alternative Communication Devices
Recent Developments in Mid-Tech Communication Solutions
Traditionally, the most common electronic augmentative and alternative communication devices were mid-tech, an umbrella term encompassing static, single, and multimessage speech-generating devices that produce a fixed number of messages. The simplest are those that play recorded voice messages with the push of a button. Although these devices were typically single- or dual-message communicators, like the iTalk2™, 59 BIG/LITTLEmack™, 60,61 and TalkingBrix™, 62 there are now variants that offer an unlimited number of output messages that play in sequence, such as BIG/LITTLE Step-by-Step™, 63 or even multiple sequences, as in the BIG/LITTLE Step-by-Step with Levels. 64
For multimessage output, static electronic communication boards offer greater flexibility. Many boards, such as the Tobii® S32, 65 GoTalk Series, 66 SuperTalker™ Progressive Communicator, 67 and the QuickTalker™ Family of Communication Devices, 68 contain multiple locations that play voice messages when selected. Some devices, such as the Tobii S32 Scan, GoTalk, and SuperTalker, also use custom-made interchangeable overlays that allow different recorded messages to play with each overlay. Other boards, such as the QuickTalker series, include multiple levels, with each level producing a new set of output messages. Although this eliminates the need for multiple overlays, the number of messages is limited, and the images associated with each frame do not change with the audio. Additionally, these boards all support touch input, but do not always accommodate switch inputs.
These mid-tech augmentative and alternative communication devices are readily available. They are easy to use and learn, making them particularly suitable for young children. 69 Although they can be portable and lightweight, they are generally bulkier and less versatile than high-tech alternatives.
Migration to Mobile Platforms: High-Tech Communication Solutions
High-tech options have become prevalent over the past 20 years, 70 as technological advances have allowed the design of dynamic augmentative and alternative communication devices. Rather than producing a single output for each input, these devices are coded, permitting multiple possible outputs for a limited number of inputs. 71 In comparison to static boards, dynamic screen communication devices provide a larger vocabulary to the user at one time, enabling more natural and responsive communication.
Until recently, the market for high-tech, dynamic augmentative and alternative communication devices was dominated by a small number of companies. 72 These companies produced a limited number of dedicated systems, or systems that could only be used for communication. 73 However, because of the mobile technology revolution, the use of mobile smart phones and tablets for augmentative and alternative communication has become widespread. 74 –76 This adaptation of mainstream hardware has created a significant paradigm shift in high-tech augmentative and alternative communication devices, as these popular communication tools offer several advantages over traditional systems, including cost, 75 –78 ease of use, 74,75,77 availability, 79 transportability, 75,76,80 and social acceptance. 69,74,75,81 Additionally, these multifunctional mobile devices provide access to mainstream phone applications, such as text messaging, e-mail, and internet browsing, which have become essential aspects of communication. 76,82,83 Table 1 presents a list of high-tech augmentative and alternative communication systems that are commercially available at the time of writing.
Growing Abundance of Apps
Because of the economic and social appeal of deploying mainstream consumer technology for communication, there has been a recent surge in the number of mobile augmentative and alternative communication applications, or “apps.” 74,75 Assistive communication apps are currently available for a variety of platforms including Android, Windows, and most popularly, iOS (Apple Inc’s mobile operating system for iPods, iPhones, and iPads). 78 Although augmentative and alternative communication users are now afforded a diversity of cost-effective, easily attainable options, most apps have been developed by programmers who do not necessarily possess knowledge in language development. 74,82 Consequently, not all apps represent language concepts in a manner that is conducive to learning and optimizing communication. Unlike devices purchased from large augmentative and alternative communication companies, 79 these apps can be easily purchased without the input of a clinician. Thus, failure to reap the anticipated benefits of augmentative and alternative communication may simply be due to a mismatch between the specific app’s functions and the individual user’s needs. Furthermore, many apps do not support connections to alternative access technologies. Unfortunately, minimal research has focused on improving the design of augmentative and alternative communication apps, even though simple design changes can often substantially impact communication performance. 83 Many app purchases are currently driven by hype, rather than an understanding of what is required to optimize communication for a specific user, information typically derived from a systematic, multidisciplinary assessment of the user’s needs and abilities. 76 Table 2 presents an abbreviated list of some popular augmentative and alternative communication apps.
Enhanced Personalization
Many augmentative and alternative communication devices and apps are now highly customizable. Features that can be personalized include vocabulary content and organization, visual appearance, and audio output. This flexibility allows the communication aid to be tailored to a specific user. However, device customization can be very time-consuming, 77 especially for apps that require the creation of all graphics and communication pages from scratch. 84 –86 Nonetheless, apps are typically more intuitive to program than dedicated communication systems. 77 Additionally, there is growing multilingual support within augmentative and alternative communication apps. At the time of this writing, some apps (eg, TalkingTILES 87 ) already provide more than 40 different language alternatives and accommodate non-English symbols. Indeed, the incorporation of language-specific grammar has been identified as a general principle for ensuring clarity of meaning in non-English augmentative and alternative communication systems. 88
Most augmentative and alternative communication systems employ symbol-based communication, in which symbols (that produce spoken words or phrases when selected) are organized into grids or lists. To continuously customize the user’s vocabulary, typically, new words or phrases can be added, as needed, and grouped topically, to form communication pages. 13 –20,84 –87,89 Pages can also link to other groups of symbols or pages to provide more extensive organization. This allows caregivers, teachers, and clinicians to personalize the system and quickly respond to changing communication needs. However, complex organizations that require navigation through multiple screens to locate the desired symbol can be overwhelming for the user, 69,83 especially for young children or individuals with cognitive impairments. Augmentative and alternative communication layouts that use simple, sequential navigation though communication pages may be more appropriate for these individuals. 21,86 The focus should be on strengthening communication and language concepts rather than simply exploiting technological advancements to enhance the complexity of augmentative and alternative communication software. 74
In addition to customizing the vocabulary, many augmentative and alternative communication devices and apps permit the visual appearance of symbols to be modified. Freedom to adjust the size of the symbols 18,19,22 can be beneficial for users with low vision. Additionally, preexisting symbols can often be replaced with new selections from the Internet, personal photographs, or built-in symbol libraries. 16,19,20,23,24,84 –87 Replacing the symbol’s image with one that better represents a language concept to a user can improve learning and communication drastically. 83 This customization inevitably limits the interuser transferability of symbol sets. Device personalization also now extends to voice output. In addition to offering a variety of realistic synthetic voice options, 13,14,16 –18,23,25 –28,87 many apps and some devices provide the option of recording voice output. 25,84 –87 Some systems or apps even offer affective and expressive variants of the same voice, such as happy and sad 18 or whining, whispering and shouting 17,23 speech output alternatives.
Shifting From Dedicated to Integrated Communication Systems
To meet the expanding scope of communication, many augmentative and alternative communication companies are now evolving their offerings from dedicated communication systems to systems that can be seamlessly integrated into the digital environs. Many of the devices produced by these companies can now be either purchased as dedicated speech generation systems or with additional computer capabilities, 13,14,16,25,29 such as Internet browsing and word processing software. Manufacturers often also facilitate mobile phone functions (ie, texting, calling) 16,25,26,30 and environmental control of infrared (IR) or Bluetooth-enabled household appliances (eg, televisions, DVD players). 13 –17,25 –27,29 This new integrated option couples the expertise and technical support of established augmentative and alternative communication companies with the increased functionality and interconnectivity offered by mobile devices. However, in some jurisdictions, current health insurance generally only covers augmentative and alternative communication devices solely running communication software 17,29,31 whereas mobile devices adapted for augmentative and alternative communication use are typically not covered by health plans. 32 Nonetheless, these mobile solutions are significantly less expensive than the multifunctional or dedicated devices sold by augmentative and alternative communication companies. In other jurisdictions, there are emerging funding programs that will reimburse, at least partially, the cost of a generic mobile device (eg, iPad or iPod) equipped with a government-approved communication app. 37
As an interesting alternative, the ComLinkProSlate™ series 34,38,42 provides a hybrid between traditional and mobile device–based high-tech communication aids. Devices within this series have the full features of a dedicated speech generation device, such as voice output modules and switch accessibility, but are loaded with one of several popular iOS communication apps. Furthermore, because they are dedicated speech-generating devices, they are fully funded by health insurance. 34,38,42
Discussion
Deriving full benefit from an access solution necessitates long-term adoption of the device. Unfortunately, abandonment of communication devices has traditionally been a significant concern. Major factors often implicated in device abandonment include an incomplete assessment of user abilities and context, 11 lack of user and communication partner training, and a poor fit between the user’s abilities and the system’s characteristics. 35 Recent trends in communication-based access solutions, however, may provide an opportunity to mitigate abandonment. Traditional access technologies based on mechanical switches are extremely difficult for some individuals with cerebral palsy to operate.36 , 50 This is an important cause of poor performance and subsequent abandonment. The increasing proliferation of new access technologies could potentially address this issue. The advent of access technologies based on eye gaze, arbitrary head or limb movements, nonspeech vocalizations, and facial expressions increases the possibility of offering access to each unique individual. However, the evidence for many of these technologies is not yet robust and largely based on case study or case series reports. Further, this proliferation of new access technologies does not come without challenges. As the range of available options grows, so too does the need for thorough, timely, and systematic assessment to identify the optimal technology for a given child. This should be a formal process that combines the opinions of and desired outcomes for parents, clinicians, and pediatric clients alike with objective measures of switch use and communication ability. 11 Some recent work has focused on formalizing such protocols, 11 invoking a multidisciplinary team that includes parents, teachers, speech-language pathologists, occupational therapists, and rehabilitation or clinical engineers. Additional research is still needed in this area.
It is also important to recognize that the appropriate access solution may change over time. As children grow, they may require new functionality from their access solution, and may be able to master more complex augmentative and alternative communication systems. They may also desire to use their access solution in a wider variety of environments. These evolving requirements have traditionally been problematic because of the limited adaptability of augmentative and alternative communication devices. The increasing availability of highly flexible augmentative and alternative communication systems (eg, apps for tablet and smart phones) should make it much easier to cope with such dynamic requirements. The significant reduction in cost also facilitates frequent switching between augmentative and alternative communication systems, so users will not be shackled to a device that no longer meets their needs, although clearly, cost is not the only enabler of augmentative and alternative communication system mastery. The shift in access solutions from specialized to general, integrated devices may promote the translation of device usage from institutions to the home environment. Moreover, the greater degree of social acceptance of smart phone and tablet-based augmentative and alternative communication devices over dedicated augmentative and alternative communication devices could also counter abandonment. 69,74,81
Certain limitations to the current state of communication access solutions must be recognized. High-tech access solutions like those detailed within this review are not suitable for all situations and environments. Practical concerns like battery power and device portability typically limit the usage of high-tech devices. Low-tech assistive technologies may address these issues, but may offer limited adaptability and scope of communication. High-tech devices for long-term usage are often susceptible to inadvertent activations. 39 These shortcomings motivate a “total communication” approach, where assistive technologies are deployed in complementarity with other modes of communication. 40
We recommend several future directions in assistive technology research for children with cerebral palsy. First, multiuser studies should be performed on emerging access technologies that have not yet been applied to individuals with cerebral palsy. These include surface microphones for detecting muscle contractions, 41 the detection of vocalizations using microphones or surface EMG, 43,90 and brain-computer interfaces based on electroencephalography or near-infrared spectroscopy. 91 –93 As existing research with these emerging modalities has been based on modest samples of children, a more extensive evidence base must be established. Second, more research must be devoted to the study of efficient communicative interaction in the context of severe disability. Caregivers have long criticized existing assistive technologies for slow and tiresome scanning protocols that frustrate pediatric users and communication partners alike, thereby heightening the risk of abandonment. Some worthwhile research and development foci may include deliberate departures from traditional single-switch scanning paradigms, such as continuous pointing gestures as invoked in Dasher 94 and investigations to enhance instantaneous machine awareness of the human-machine interaction through, for example, the exploitation of event-related potentials on a single-trial basis. 95 –97
Conclusions
This study has identified some emergent trends in access technologies and augmentative and alternative communication devices that are used in communicative access solutions for children with cerebral palsy. Access technologies have evolved from direct physical activation and simple mechanical switches to custom-placed sensors that are less dependent on gross motor control. Numerous access technologies have emerged, including eye-gaze tracking, thermal cameras, microphones, and pressure sensors.
Augmentative and alternative communication devices have progressed from bulky electronic systems with limited message output to vocabulary-rich, highly customizable, portable alternatives. Augmentative and alternative communication devices are trending toward mobile and tablet applications that are more affordable, readily available, easier to use, and even socially acceptable. However, augmentative and alternative communication apps do require time to customize, and, with the numerous options now available, identifying the most suitable augmentative and alternative communication device for a given child is often a daunting task. Future research must focus on the development of more effective and intuitive user interfaces, validation of access technologies and augmentative and alternative communication devices with larger populations, and the development of a formal process for choosing the optimal access solution.
Key Take-Home Messages
Access technologies are expanding, in earnest, beyond traditional mechanical switches. Technologies based on inertial sensing, machine vision and physiological signals are showing promise with small samples of individuals with cerebral palsy and other neurodevelopmental conditions.
Augmentative and alternative communication systems are shifting from dedicated hardware to ubiquitous, socially appealing mobile devices and mainstream operating systems. In parallel, there has been a heavy precipitation of communication apps that provide enhanced device personalization (images, vocabulary, voice output, languages) at a fraction of the cost of traditional augmentative and alternative communication systems.
Evidence for the effectiveness of these access technology and augmentative and alternative communication system developments is largely case-based at present, but mounting rapidly.
In light of the above, the introduction of access technology ought to be considered for children and youth with at least nascent contingency awareness, even in the presence of sensory and/or severe motor impairments, which preclude the use of conventional mechanical switches.
Footnotes
Author Contributions
AM, SW, LS, and TZ conducted the literature search and wrote individual sections of the manuscript. TC conceptualized the manuscript, helped to consolidate the various pieces, edited manuscript drafts, and revised the manuscript according to reviewer comments.
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.