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Control Interfaces for Assistive Technology. Hsin-yu Chiang, ScD, OT. Learning Objectives. Describe the elements of Human/Technology interface Describe the characteristics of Control Interfaces Learn how to select Control Interfaces for the users Identify technologies for direct selection

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Learning Objectives

  • Describe the elements of Human/Technology interface
  • Describe the characteristics of Control Interfaces
  • Learn how to select Control Interfaces for the users
  • Identify technologies for direct selection
  • Identify technologies for indirect selection
  • Other considerations

Elements of Human /Technology interface

●Control Interface: input device

discrete inputs (computer keyboard), continuous inputs (mouse)

● Selection Set

Visual (computer keyboard), tactile (braille), auditory(spoken choices)

●Selection Methods

Direct selection, indirection selection

● The processor:connecting the interface to the

activity output

Generate feedback & activity output


Characteristics of Control Interfaces

●Spatial characteristic: placement and size of CI

Its overall size, weight & shape; no. of target within CI; size of target; spacing between target….

● Activation & Deactivation characteristic: how it

is activated?

  • Method of activation:

Movement (eye, head, tongue)

Mechanical CI:keyboard, joystick..

Electromagnetic CI:light detector, IR remote

Electrical CI: EMG

Proximity CI: heat sensitive switch


Respiration (inhalation-expiration): puff & sip

Phonation: sound switch, speech recognition……

  • Other activation characteristics:

Effort, displacement deactivation flexibility durability & maintainability

● Sensory characteristic: what feedback is obtained?

Auditory: click sound Somatosensory: tactile, kinesthetic, propriceptive Visual: color


Select Control Interfaces for the users

Outcomes of Needs Identification

Outcomes of Physical-Sensory Evaluation

Control Enhancers


Indirect selection



Control Interfaces for Direct Selection

● Most rapid, preferred over the use of indirect selection

● Some critical questions to ask for keyboard using

  • Can c’t reach all of the key?
  • How about the accuracy? At least 75% be correct
  • How about the speed?

● Some alternative keyboards

Expanded keyboard, contracted keyboard, touch screen, tongue-touch keypad………..


These keys are not assigned

  • any specific functions when
  • manufactured,but can be
  • programmed just about
  • anything the user like.

AlphaTalker (special purpose keyboard)


Head-Controlled Computer Access

  • Three-Dimensional Tracking Systems
  • Features:
    • Wireless Operation (senor attached to the forehead)
    • No Cumbersome Head Mounted Apparatus
    • Precise Pointing
    • Operates in Conjunction With or Replaces
    • Standard Desktop Mouse

Speech Recognition System

  • Speaker dependent system
  • Recognition depends on the
  • system’s learning the user’s
  • speech pattern
  • Speaker independent system
  • No training required
  • Vocabulary set is small, used in
  • ECU & powered mobility

Control Interfaces for Indirect Selection

  • Using a single switch or an array of switches
  • The c’t needs to :
  • activate the switch and activate at right time
  • wait for the desired selection to be presented
  • hold the switch
  • release the switch
  • Selection techniques for scanning
  • automatic scanning
  • step scanning
  • inverse scanning

Selection Formats for scanning

  • Linear
  • Rotary
  • Coded access
  • Morse code

rotary scanning



Types of single switches

Paddle switch

Wobble switch

Leaf switch

Lever switch


Other considerations

  • Integrated control: Use the same interface for
  • several applications
  • Mounting system
  • Flexible
  • Fixed

Flexible mounting system