Cole Assistive Tech Chapter 6

A reliable and systematic method for selecting the most appropriate scan rate for single-switch scanning that avoids excessive trial and error is provided by the

"0.65 rule" The 0.65 rule is based on data showing that the ratio between a user's reaction time and an appropriate scan rate for that user is approximately .65 The clinical implication is that if the consumer's reaction time can be measured, then dividing this number by 0.65 will give a scanning rate in scan per seconds that is likely to be the optimal rate for that person.

Word completion can reduce the item selection rate compared with letter-by-letter typing. This reduction in selection rate is due to

"cognitive or perceptual load" that can offset the benefits achieved in keystroke savings and result in an overall decrease in text generation rate (Hortsman & Levine, 1989). There are also cognitive demands placed on the user by the way in which the rate enhancement is implemented. Predictions are easier to use because they do not require memorization of codes

Two methods of correcting for this type of error were modeled by Simpson et al.:

(1) a fixed loop count as earlier and (2) a "continue scanning" item at the end of the row that is selected to restart the scanning through the row.

Rate enhancement techniques fall into two broad categories:

(1) encoding techniques and (2) prediction techniques. Vanderheiden and Lloyd (1986) distinguish three basic types of codes: memory based, chart based, and display based. These are compared in Table 6-3.

The processor interprets the information and generates two signals that are converted to

(1) feedback to any display that is being used and (2) an activity output, depending on the functions of the AT system. The selection set must include an element corresponding to each function of the device.

Simpson et al. (2011) developed an approach that models errors and includes several types of error correction commonly applied in scanning systems when an incorrect switch activation is made by the use.

(1) setting a fixed number of times for the scanning to loop through the row or column or the array before starting over at the beginning (fixed loop count), (2) a stop scanning selection at the end of each row, (3) activating the switch for an extended time, and (4) selecting an (incorrect) item within the row. In addition to these errors of commission, there is the error of omission in which the user fails to make a choice in a row.

The development of motor skill for the operation of one or more control interfaces can also have carryover into more general motor skill development. Three outcomes can be achieved by a motor training and practice program:

(1) the individual can broaden his repertoire of motor capabilities and the number and type of inputs that can be accessed; (2) the individual can refine the motor skills she has in using an interface to increase speed, endurance, or accuracy; and (3) the individual who lacks the motor skill to use any interface functionally can develop these skills.

Based on their model results, they concluded that the best approach for clinicians is to:

(1) use a frequency-arranged matrix, (2) avoid extra "bells and whistles" such as stop scanning or reverse scanning items, and (3) keep error rates as low as possible by focusing on development of switch skill as we describe later in this chapter.

Selection sets can be represented by

- traditional orthography (e.g., written letters, words, and sentences), - symbols used to represent ideas, computer screen icons, line drawings, or pictures.

Approximately 8000 morphs can generate more than

95% of the words in English. To break words down into morphs and then match the morphs to the speech sounds requires the development of a text-to-speech system.

Selection Methods

An approach allowing the user to make choices from the selection set; includes scanning, directed scanning, and coded access

Direct Selection

An approach in which the individual is able to use the control interface to randomly choose any of the items in the selection set Directed scanning is a hybrid approach in which the user activates the control interface to select the direction of the scan, vertically or horizontally. When the switch is released, the cursor stops, and the user either waits for an acceptance time interval or hits an additional switch

Inverse Scanning

An approach in which the scan is initiated by the individual's activating and holding a switch closed, with selection of the desired item indicated by releasing the switch; entry is by an additional switch press or acceptance time For individuals who require lots of time to initiate and follow through with movement, inverse scanning can be helpful motor fatigue is reduced over step scanning because of fewer control interface activations; however, sensory and cognitive fatigue are higher because of the vigilance required to attend to the display.

Rotary Scanning (circular scanning)

An approach in which the selection set is organized in a circular pattern

Linear Scanning

An approach in which the selection set is organized in a linear (straight-line) format

Directed Scanning

An approach in which the user activates the control interface to select the direction of the scan, vertically or horizontally, and then sends a signal to stop at the desired choice; entry is by an additional switch press or acceptance time

Step Scanning

An approach in which the user activates the switch once for each item to move through the choices in the selection set; entry is by an additional switch press or acceptance time Step scanning allows the user to control the speed at which the items are presented The ability to activate the control interface repeatedly, however, is important for step scanning. Motor fatigue can be high because of repeated control interface activation.

Indirect Selection

An approach in which there are intermediary steps involved in making a selection; includes scanning, directed scanning and coded access; typically the control interface used is a single switch or an array of switches

Group-Item Scanning

An approach that is used to increase the rate of selection during scanning by grouping the selection set and allowing the user to first select a group and then the desired item in the group When there are a large number of items, a matrix scan can be used. In this type of scanning, the group is a row of items and the items are located in columns, and it is called row-column scanning.

Abbreviation Expansion

An augmentative and alternative communication or computer access technique in which a shortened form of a word or phrase (the abbreviation) stands for the entire word or phrase (the expansion); abbreviations are automatically expanded by the device Abbreviations are more direct because the user can merely enter the code and immediately get the desired word, and they allow complete phrases and sentences.

continuous input

When the inputs of a device are ongoing, with an infinite number of possible values (e.g., volume control on a radio)

When an individual has limited upper extremity fine motor control, it is necessary to use

alternative anatomic sites such as head movement or gross arm, hand, or leg movements. training and practice is required to develop the necessary skills.

The physical context can also provide challenges. All selection systems that rely on visual displays are sensitive to

ambient light conditions, especially bright sunlight. The physical space and ability of the space to support proper positioning for access is another physical context issue

Development of Skills for the Use of Control Interfaces

an individual may have a control site and the ability to activate a single switch, but the ability to activate this control interface is not consistent enough to justify the purchase of an assistive device such as a wheelchair, computer, or augmentative communication system. The intervention then becomes one of improving the individual's motor control so she will be able to reliably activate the control interface.

Prosodic Features

aspects of speech that give it a human quality, generated by changes in amplitude, pitch, and duration Murray et al. (1991) developed software, called Hamlet, that used DECTalk (Fonix Corporation, Sandy, UT; http://www.fonix.com) speech synthesizer voice quality to provide vocal emotion effects to the synthetic speech.

Speech is the

auditory form of language, and electronic ATs that provide language output rely on artificial speech.

Gross motor skills include

balance on one foot, performing symmetrical and asymmetrical movements of the upper and lower extremities; coordinating one side of the body; lifting and carrying objects; rapidly alternating movements; and running, skipping, and hopping.

Automatic scanning can be difficult for individuals with spastic CP, and step scanning is difficult for those with athetoid CP (Davies et al., 2010). There is no conclusive evidence regarding the

best method for each group.

The Gross Motor Function Measure (Russell et al., 2002) is designed specifically for

children with neurological impairments.

Selection of control interfaces for a given individual depends on

cognitive and motor requirements presented by a particular interface as well as the skills of the individual in these areas

Activity outputs in the HAAT model include

communication (replacing or augmenting speech or writing), mobility, manipulation (e.g., things we would normally do with our hands and arms), and cognition (assisting with mental activities)

Bailey (1996, p. 173) defines an interface as "the boundary shared by interacting components in a system" in which "the essence of this interaction is

communication or the exchange of information back and forth across the boundary

The Bruininks-Oseretsky Test of Motor Proficiency (Bruininks & Bruininks, 2005) and the Movement ABC (Henderson et al., 2007) are two examples of

comprehensive motor evaluations appropriate for children.

Control interfaces are typically used by individuals who have reduced fine motor control that makes it difficult to use common HTIs such as

computer keyboards, pointing devices such as a mouse, or touch screens; light switches; controls on entertainment devices such as TVs or DVD players; and similar everyday items. Control interfaces are also useful to people who need to use a powered wheelchair or use adapted controls to drive a vehicle

Control interfaces that can detect sound and speech recognition can also be used as a

control interface. Tongue movements can also be used for control.

the HTI describes the way in which the human

controls the device.

Gross and fine motor assessments generally test

higher level motor skills.

If the consumer has the potential for reliable hand use, it is then necessary to determine the

minimal and maximal arm range within a workspace and the resolution in hitting a target. A range and resolution board, as shown in Figure 6-15, can be used to measure both of these.

Performance by typically developing children was related to age and gross motor abilities. In addition to these, performance of children with iintellectual disabilities was also related to

pattern analysis skills, and the individual input devices showed distinctly different relationships to cognitive and motor development than for the typically developing children.

When the control interface is activated by the user, information is sent via a signal to the

processor.

Fine motor assessment includes

rapidly alternating finger movements, performance of isolated finger movements, manipulation of objects of different sizes, and performance of specific fine motor tasks.

Telephone lines have a narrower bandwidth (frequency range), which affects the amount of distortion and the quality of the speech. The use of speech synthesis and the intelligibility of speakers with dysarthria are therefore

reduced over the telephone

Direct selection is the most difficult method physically because it requires

refined, controlled movements. Because there is an immediate, direct result from the selection made, it is more intuitive and easy to understand, and the cognitive demands are not great.

The three major AT applications are

screen readers and print-material reading machines for persons who are blind, voice output augmentative communication devices, and alternative reading formats for persons with cognitive disabilities.

If both hand and head control are poor, then control interfaces, generally switches, can be used to detect movements of the

shoulder, elbow, forearm, hand, or finger.

Finally, respiratory air flow can be detected and used as a control site by

sip (inhaling) or puff (exhaling) to access switches.

Over the telephone, speech quality is degraded more for the natural dysarthric speaker than for the speech synthesis, and the listeners clearly preferred the

synthetic speech.

Scanning is inherently slow. A major challenge in scanning is maximizing the scan rate. If the rate is too fast, users will not be able to make accurate selections because they cannot respond fast enough. If the rate is too slow, the

text entry rate (TER) will be slower than necessary and cause the user to be slower at generating input than is necessary.

Again, if a neurologic condition is present, it is important to remember that function depends on the client's position.

the client's position.

Three technology elements of the HTI contribute to the operation of a device:

the control interface, the selection set, and the selection method. These three elements are interrelated, and careful attention must be given to each element to have an effective HTI.

Dysarthria

the inability to use speech that is distinct and connected because of a loss of muscle control after damage to the peripheral or central nervous system

Similar to scanning, coded access requires less physical skill than direct selection. The advantage of coded access over scanning, however, is that

the timing of the input is under the control of the user and is not dependent on the device.

Simulation of functional tasks is used to evaluate the types and quality of movement an individual possesses. Functional tasks are chosen for evaluation because

they are often more meaningful to the consumer than physical performance components such as strength and joint range of motion. They also provide the clinician with an opportunity to gather qualitative information regarding the consumer's movements, and results of such tasks are more likely to reflect the consumer's true abilities.

The modalities in which the selection set is presented can be

visual (e.g., letters on the keyboard or icons on the screen), tactile (e.g., braille), or auditory (e.g., spoken choices in auditory scanning).

Another control site is foot movement. For fine manipulative tasks, the foot is less desirable than the hand or head because

visual monitoring can be difficult, and the foot is generally not as finely controlled as the hand.

Control sites

The body sites that can be used to control a device.

The human/technology interface (HTI) is a major part of the assistive technology component of the

Human Activity Assistive Technology (HAAT) model

digital recording

Human speech is stored in electronic memory circuits for later retrieval The major advantage of digital recording of speech is that it allows any voice to be easily stored in the device and played back. For example, if the person who is using the AAC system that uses digital recording is a young girl, we can use another young girl's voice to store the required messages.

Three contexts affect the HTI as we have described in this chapter.

In the social context, the use of ATs can be stigmatizing for the individual using it. The slow speed may significantly change the social interaction a person has. Artificial speech can also be stigmatizing.

Automatic Scanning

Items are presented continuously by the device at an adjustable rate (scan rate), with selection of the choice made by activating the switch and stopping the scan; entry is by an additional switch press or acceptance time.

Row-Column Scanning

A form of group-item scanning in which the items are arranged in a matrix and the row is first selected by a switch press, then the item is selected from that row by a second switch press; entry is by an additional switch press or acceptance time.

Coded Access

A form of indirect selection in which the individual uses a distinct sequence of movements to input a code for each item in the selection set Morse code is one example of coded access, wherein the selection set is the alphabet but an intermediate step is necessary in order to obtain a letter

Acceptance Time

A method used for selection of an item in a scanning system that is based on the user's pausing for a preset period, after which the entry is made

Word Completion

A technique that displays stored words on the basis of the sequence of entered keys; the user selects the desired word, if any, by entering its code (e.g., a number listed next to the word) or continuing to enter letters if the desired word is not displayed

Most AAC devices and screen readers for the blind use

DECTalk, Eloquence or Vocalizer, AT&T Natural Voices, IVONA, Acapela, or a proprietary text-to-speech system. TMA Associates (Tarzana, CA; http://www.tmaa.com/) provides listings and analysis of text-to-speech and other related products. Aaron et al. (2005) provide an excellent overview and tutorial on speech synthesis.

Anatomic sites commonly used for control of assistive technologies. (From Webster JW, Cook AM, Tompkins WJ, Vanderheiden GC: Electronic devices for rehabilitation, New York, 1985, John Wiley and Sons, p. 207.)

Each control site is capable of performing a variety of movements or actions.

If fine motor control limitations prevent hand use, then the use of the ___blank___ as a control site is preferred.

Head. It is possible to obtain relatively precise control using head movements such as tilting side to side, horizontal rotation, and linear forward and backward movement. Very few functional head movements are purely horizontal, vertical, or rotational.

____Blank_____ may produce sounds (including whistling) or speech.

Phonation

Text-to-Speech Programs

Programs that analyze a word or sentence and translate it into the codes required by a speech synthesizer The most common approach is to break words into syntactically significant groups called morphs, store sound codes associated with each morph, and match the morph to the letters typed.

Speech Synthesis

The generation of human-sounding speech by use of electronic circuits and computer software This approach reduces the amount of memory required. Speech output can be created from any electronic text, including that sent to the screen of a computer or mobile device

A Clinically Based Framework for Determining Optimal Anatomic Sites for Accessing a Control Interface

The hands, being the control site of choice, are the first to be assessed. Basic hand function can be observed and rated by using a "grasp module" (Figure 6-14) that includes a total of seven functional grasp patterns.

Control Interface

The hardware (e.g., keyboard, joystick) by which the user operates an assistive technology system or controls a device. It is s times also referred to as an input device.

OUTCOMES Optimal Control Sites

The initial evaluation may only indicate potential control sites that may be developed with practice or anatomic sites that are easily controlled without additional training and practice. Because it is also possible that the person's skills may decrease over time in the short term during the day because of fatigue or in the longer term because of a degenerative disease, identifying a "back-up" control site is a useful strategy when possible.

Selection Set

The items available from which user choices are made; in augmentative and alternative communication devices this is the component that presents the symbol system and possible vocabulary selections to the user For example, if a person wants to use a power w-chair, the selection set might be forward, back, left, right, and stop.

Scanning

The most common indirect selection method in which the selection set is presented by a display and is sequentially scanned by a cursor or light on the device, with the user selecting the desired choice by pressing a switch when it is indicated by the display; entry is by an additional switch press or acceptance time Scanning requires good visual tracking skills, a high degree of attention, and the ability to sequence. The advantage of scanning is that it requires very little motor control to make a selection.

Indirect scanning

The person indicates her choice by using voice, finger, hand, eye, or other body movement. In this method of selection, the user identifies a target and goes directly to it

Command Domain

The set of assistive device functions available to the user

There are other ways that scanning formats can be adapted to increase the user's rate of selection. Halving is

a group-item approach in which the total array is divided in halves. This same concept can be used in a quartering format in which the array is divided into fourths.

The size, modality, and type of selection set chosen are based on the user's needs and the desired

activity output

The two types of speech output are:

digital recording and speech synthesis. They differ in the manner by which the speech is electronically produced. Table 6-4 lists the features and the typical AT applications for the two approaches.

There are two basic selection methods that an individual with a disability can use to make selections with a control interface:

direct selection and indirect selection.

the institutional context, HTI devices can be

expensive, and the process of obtaining funding can be complex.

Adult listeners heard mildly (90% intelligible) dysarthric spoken speech and synthesized speech in both

face-to-face and telephone contexts.

Another method used to increase rate of selection is to place the selection set elements in the scanning array according to their

frequency of use. For example, if letters are being used as the selection set, placement of E, T, A, O, N, and I (the most frequently used letters) in the upper left positions of the scanning array results in an increase in rate of selection (Simpson, 2013)

The smallest meaningful units of language are called

morphemes. Free morphemes are complete words that may stand alone (e.g., run); bound morphemes must be coupled to another morpheme (e.g., -ing) to form a complete word.

The commonly used system, DECTalk, uses

morphonemic principles of speech synthesis (Bruckert, 1984).

The overall goal of the physical skills evaluation is to determine the

most functional position for the individual and evaluate his or her ability to access a device physically. At a very basic level, physical skills include range of motion, muscle strength and endurance, muscle tone, and the presence of primitive reflexes and reactions.

Automatic scanning requires a high degree of

motor skill by the user to wait for the desired selection and to activate the control interface in the given time frame. It also requires a high degree of sensory and cognitive vigilance for attending to and tracking the cursor on the display.

Skill development varies greatly across different input devices depending

on cognitive load, mastery, speed, and user characteristic.

If the hands are eliminated as a control site,

other anatomic sites must be considered