«Assistive Technologies for Spinal Cord Injured Individuals A Survey Tiago Jo˜o Vieira Guerreiro a 6648/M Assistive Technologies for Severe Spinal ...»
Instituto Superior T´cnico
Mestrado em Engenharia Inform´tica e de Computadores
Assistive Technologies for Spinal Cord
Tiago Jo˜o Vieira Guerreiro
Assistive Technologies for Severe Spinal Cord
Injured Individuals: A Survey
Spinal cord injured (SCI) individuals are often deprived from computer
access and subsequent control and communication abilities. Their motor skills
loss often translates in the inability to operate traditional inputs like the keyboard and mouse pointer devices. Moreover, with the enormous technology evolution in the last few years, our lifes, control and communication depend increasingly on gadgets (i.e., mobile devices). More than just leisure, jobs depend on those technologies. This technological evolution, contrary to what could be expected, has enlarged the damp between disabled and fully-capable individuals and indirectly reduced their life quality. In the past decades several approaches have been made to overcome this problem and re-approach SCI patients to computers or any other electronic device. In this report we review the major approaches to assistive technologies considering spinal cord injured individuals, discussing and comparing both their advantages and limitations.
Contents 1 Introduction 1
1.1 Spinal Cord Injury............................ 1
1.2 Motivation................................. 2
1.3 Assistive Technologies.......................... 3
1.4 Interfacing Schemes............................ 4
1.5 Evaluation and Assessment Criteria................... 5
1.6 Document Overview........................... 8 2 Touch Switches, Sticks and Pointers 12 3 Sound-Based Interfaces 17 4 Gaze and Motion Tracking Interfaces 27 5 Myographic Interfaces 42 6 Brain-Computer Interfaces 49 7 Breath-Based Interfaces 55 8 Overall Discussion 59 9 Conclusions
Technology is creating new opportunities for more than 60% of Europe’s population, connecting us to better paid jobs, instant information, new forms of social interaction, community infrastructures, government services, consumer power and convenience. It plays an ever increasing role in our day to day lives - in how we communicate, how we carry out business, how we acquire information and how we enjoy ourselves. It touches our lives in ways which we are often unaware of or do not event think about. - In e-Inclusion Ministerial Debate 2007 Conference Guide We are used to communicate with computers through keyboards and mouse pointer devices. Although several non-conventional input modalities appeared in the last few years the traditional approaches are still overwhelming. For any physically fullcapable individual there are several input modalities to choose from and it is a personal choice to use keyboards and mouse pointer devices to operate with computers. A part of the population, due to physical impairments, isn’t able to choose and is often incapable of operating with electronic devices. Severe spinal cord injured individuals are a part of this group presenting disabilities that deprive them to operate traditional modalities.
1.1 Spinal Cord Injury
The spinal cord is the largest nerve in the body extending from the brain to the waist.
The nerve ﬁbers inside the spinal cord carry messages between the brain and other body parts to enable sensory, motor and autonomic functions. The nerves within the spinal cord, named upper motor neurons, carry messages back and forth between the brain and the spinal nerves. The nerves that branch out from the spinal cord, named lower motor neurons, carry sensory information and motor commands between the spinal cord and other areas of the body.
These nerves exit and enter at each vertebral level and communicate with speciﬁc areas of Figure 1: Spinal Cord the body (Figure 1).
Spinal cord injury (SCI), or myelopathy, is a disturbance of the spinal cord that results in loss of sensation and mobility. Spinal cord injuries can aﬀect the communication between the brain and the body systems that control sensory, motor and autonomic function below the level of injury. It is important to note that the spinal 1 cord does not have to be completely severed for there to be a loss of function. In fact, the spinal cord remains intact in most cases of spinal cord injury. In general, the higher in the spinal column the injury occurs, the more dysfunction a person will experience.
The eight vertebrae in the neck are named cervical vertebrae. The top one is called C1 and the next C2. Injury of cervical nerves between C1 and T1 (ﬁrst thoracic vertebrae) could result in tetraplegia (formerly called quadriplegia). Depending on its vertebral level and severity, the individuals with tetraplegia experience a loss of motor and/or sensory functions in their head, neck, shoulders, upper chest, arms, hands and ﬁngers. Injury between C1 and C4 is usually called high tetraplegia, while injury between C5 and C8 is called low tetraplegia. A person with low tetraplegia may still have partial motor/sensory function in his shoulder, arms, and wrists.
Injury between T2 and S5 could cause Paraplegia (Figure 2). Depending on the severity of the SCI, individuals with SCI may experience complete or incomplete loss of motor/sensory function below the level of injury. The exact eﬀects of a spinal cord injury vary according to the type and level injury, and can be organized
into two types:
• In a complete injury, there is no function below the level of the injury. Voluntary movement is impossible and physical sensation is impossible. Complete injuries are always bilateral, that is, both sides of the body are aﬀected equally.
A person with an incomplete injury retains some sensation below the level of the injury.
• Incomplete injuries are variable, and a person with such an injury may be able to move one limb more than another, may be able to feel parts of the body that cannot be moved, or may have more functioning on one side of the body than the other.
1.2 Motivation The limitations imposed by spinal cord injuries deprive the injured individuals from operating electronic devices like computers or mobile devices. Besides the drastic quality of life reduction directly imposed by the impairments, individuals also face a communication shutdown as they are often incapable of operating devices that make possible to communicate with others (computer, cell phone, PDA).
Moreover, as new technologies appear and communication channels increase, the damp between full-capable individuals communication capabilities and the severely disabled ones also increases. The technological evolution inﬂuences negatively the disabled population as their inhability to operate and communicate with the new technologies damages the social interaction but also their integration within the society as active members and, particularly as workers who also need to guarantee survival.
1.3 Assistive Technologies Assistive Technology is a generic term that includes assistive, adaptive, and rehabilitative devices that promote greater independence for people with disabilities.
Computer control and the subsequent electronic device or even ambient control is a actual world wide concern because it oﬀers people with disabilities the ability to improve their quality of life. Actually through computer control several others devices can be actuated and by that means oﬀering disabled higher freedom and independence levels.
The ability to operate a PC is extremely valuable nowadays, particularly for persons with disabilities. Among other things, the computer can be used to access the Internet, read or compose emails, listen to music, watch movies, or play games.
Given the right interfaces, computers can even control a mobile robot or an electricpowered wheelchair, as well as switch lights or other appliances on and oﬀ. To say the least, a computer can help very much with the integration of disabled individuals into society.
Unfortunately, the standard way of operating a PC requires the reliable use of hands and arms, since it involves a keyboard and a manual mouse device, which is unsuitable for a large number of people with disabilities. Therefore, developing an alternative user interface, which does not require manual input, is of great importance.
3 This fact is even more drastic when we consider mobile devices where other variables appear.
For individuals with high tetraplegia, input sources for human-computer interface are limited. Possible input sources include head movements, voice, eye movements, or muscles on the face. For individuals with a lower injury degree some other options can be explored accordingly to the individuals disabilities, like hand joysticks, switches or even monitoring arm muscles.
1.4 Interfacing Schemes
According to (Cook and Hussey, 2002), the human/technology interface is composed by three elements that contribute to the operation of the device: the control interface, the selection set and the selection method. The control interface (i.e., keyboard, switch) is the hardware by which the user operates the device while the selection set is the items available to select from (i.e., icons, letters) and the selection method is the way the user makes selections using the control interface.
Considering selection method or interfacing scheme, we consider two diﬀerent approaches: direct selection, indirect selection (scanning and coded access).
Direct selection involves a one to one correspondence between input acts and selections (i.e., QWERTY keyboard). In this method, the user identiﬁes a target in the selection set and goes directly to it. As an example of direct selection, we can mention the traditional QUERTY keyboard typing. Obviously, direct selection methods oﬀer a direct correspondence between selections and actions thus it is normally easier to use and quicker. On the other hand, if a selection set is large and the control interface (selected accotdingly to the user’s capabilities) has a reduced communication bandwidth, direct selection is not usable.
Scanning entails oﬀering the user, sequentially or otherwise, selection alternatives until the user has indicated his choice. Scanning input is widely exploited in cases of severe disability, since it remains feasible even when a user is only capable of single switch operation (Damper, 1986). In this scenario, even with a large selection set and a reduced communication bandwidth, the user is able to operate the device and accomplish the desired task.
Encoding employs a speciﬁc pattern of input acts to make a given selection (i.e., Morse code - Figure 3). In coded access, the user uses a distinct set of actions to input a code for each item in the selection set. Like scanning, coded access requires less physical capabilities than direct selection (Cook and Hussey, 2002). However, in an encoding scenario, the control is on the user side while in a scanning scenario, the device times and controls the interaction.
The choice of an assistive technology must consider this three components and must always be focused on the user and his needs. Almost all devices permit access though
4 Figure 3: International Morse Code
any type of control interface and selection method. Moreover, the selection set can be adapted to the user.
Although this document follows a control interface-based organization, the research projects and available products’ description takes the possible selection set and selection method into account. In fact, the connection between a control interface, selection method and selection set deﬁnes the human-technology interface eﬀectiveness.
1.5 Evaluation and Assessment Criteria
To select an appropriate assistive technology several factors must be considered. The level of impairment strongly inﬂuences the decision but residual capacities should also be taken seriously into account as a good matching between the user and the selectd modality can highly inﬂuence his life quality. For example, it is important to notice that individuals with low tetraplegia, with restricted but residual ﬁnger and arm motion, can be provided with some keyboard adaptations to achieve its control with no need for an extra entry interface (i.e., a Keyguard (Figure 4) for individuals with ﬁnger function compromised who are willing to make several typing errors).
On the other hand, for the most severe injuries an extra computer communication channel must be supplied.
When selecting an input device and interfacing scheme it is very important for clinicians, technologists, caregivers and the disabled themselves to be aware of the assistive technologies characteristics and their suitability to speciﬁc cases (Bates, 2002). In this survey, we present the main approaches on assistive technologies
considering SCI, reviewing the state of the art on Switches, Tracking, Electrophysiological, Speech, Hybrid as well as other less explored approaches. We present the
methods’ advantages and disadvantages comparing them considering:
Potential users range (Card et al., 1990) argued that the manipulation and control requirements of an input device maybe mapped using a design space (Bates, 2002). Considering a certain input modality we can also argue its suitability to a certain person according to the input requirements and the person’s sensory and motor characteristics. Thus it is possible to create a map that relates physical abilities with a certain input modality. This is the most important feature of an assistive technology as it presents the total inability of relations between certain impairments and input modalities. All the other features are complementary and can help a certain user to select an assistive technology from the available range, considering his disability and the desired interaction scenarios. We will refeer to the disability level but also include details on required capabilities as the spinal cord lesion level can sometimes be misleading (i.e., incomplete spinal cord injuries).