Abstract
As the number of individuals without physical access to communication or environmental interaction escalates, there are increasing efforts to uncover novel and unconventional access pathways. In this chapter, we introduce three emerging access technologies for individuals with severe disabilities: near-infrared spectroscopy, electroencephalographic measurement of visually-evoked potentials and infrared thermographic imaging of the face. The first two technologies harness activity directly from the brain while the third exploits spontaneous temperature changes in the face. For each technology, we discuss the physiological underpinnings, the requisite instrumentation, the scientific evidence to date and the future outlook.
TopIntroduction
Personal autonomy in the context of physical chronic illness can be conceptualized as the correspondence between the desired and actual life of an individual (Mars et al., 2008). To achieve this correspondence, Mars et al. (2008) asserts that individuals need to “develop principles expressing what their lives to be like” (p. 345) through daily interactions, choice-making and experiences. However, many individuals do not have physical access, due for example to an environment that does not support the functional capability of the individual. A lack of access severely limits one’s daily interactions, choice-making and social experiences and thus impinges upon personal autonomy. To restore a level of correspondence, a common approach in rehabilitation is to augment the opportunities for interpersonal connection through an access solution.
An access solution provides a means of interacting meaningfully with one’s milieu (people and objects within the environment) when functional speech or movements are not available, due for example to severe motor impairments. Often times access solutions are technology-mediated. In such case, the technical components of an access solution include an access technology and a user interface technology (Tai et al., 2008) as depicted in Figure 1. The access technology comprises of (a) an access pathway, that is, the input devices by which an expression of functional intent (e.g., a movement or physiological change) is translated into an electrical signal, and (b) a signal-processing unit that analyzes (e.g., filtering and pattern classification) the input signal and generates a corresponding control signal. The control signal in turn operates a user interface, which may be an iconic display for an electronic communication aid, a front panel for an environmental control unit, or an on-screen keyboard running on a computer.
Figure 1. Components of a technology-mediated access solution
The objective of this chapter is to introduce the reader to three nascent access technologies for individuals with severe disabilities, namely, near-infrared spectroscopy, electroencephalographic measurement of visually-evoked potentials and facial infrared thermography. While these pathways are in the pre-clinical research stages, existing scientific evidence supports their continued development into viable body-machine interfaces.
TopBackground
A Growing Population without Access
The incidence of severe and multiple disabilities (concomitant profound sensory, physical and speech impairments) among children has been increasing globally (Tudehope et al., 1995). This upward trend is expected to continue into the foreseeable future due to improved early identification of disabilities (Rumeau-Rouquette et al., 1997), increased life expectancy of medically fragile children with multiple disabilities (Jeppesen et al., 2003; Eagle et al., 2002) and higher survival rates of very low birth-weight, premature infants, the majority of whom develop disabilities (Goldson, 1996). According to United Cerebral Palsy (www.ucp.org), there are annually 5,000 new cases of children born in Canada and the USA with severe physical involvement.
An elusive challenge in the education and care of this population is the identification of a reliable access solution (Beukelman et al., 2000). Most of the individuals described above do not have functional speech, nor any repeatable volitional movements or overt physical responses. As a result, there is no obvious channel through which they may interact with teachers, caregivers, family members and peers.
Key Terms in this Chapter
SSVEP: Steady state visually-evoked potential. The measurable brain potential that naturally occurs in response to the observation of a persistent oscillating visual stimulus. The measured potential possesses a distinct spectral component at the frequency of the stimulus oscillation.
Access Pathway: The actual sensors or input devices by which an expression of functional intent (e.g., a movement or physiological change) is transduced into an electrical signal.
Stimulus Onset Visually-Evoked Potential: A measurable brain potential that is time-locked to the instant of change in the visual stimulus. The change may be associated with the initiation of motion or flickering, in which case the potential is respectively named the motion onset visually-evoked potential (MVEP) and flash onset visually-evoked potential (FVEP).
Augmentative and Alternative Communication (AAC): Refers to the strategies and approaches to enhance or substitute speech or writing and range from no-tech solutions such as hand gestures, to low-tech alternatives such as paper-based picture boards, all the way to high-tech devices such as electronic, multi-input tablets with synthesized voice output.
Environmental Control Unit (ECU): Typically an interface technology that accepts one or more user control signals (through an access technology) as input commands to operate electrical (e.g., lights, electric door-openers) or electronic appliances (e.g., television) in one’s living environment.
Access Technology: A technology that captures an expression of functional intent (e.g., physical movement or physiological change) from the user via sensors, and processes the ensuing electrical signal into a control signal that drives some user interface (e.g., AAC, ECU or computer). The access technology encompasses an access pathway and a signal processing block.