Control Interfaces
Discuss the purpose and use of control enhancers
Control enhancers enhance and extend a client's range and resolution skills. Control enhancers may enable a client to use a faster direct selection input instead of an indirect selection device. They also make tasks easier to complete and minimize fatigue. Devices such as mouthsticks, pointers and arm supports are one type of control enhancer. Joysticks may include a tremor-dampening feature, meaning the joystick distinguishes between deliberate movements and tremors. Both mobile arm supports and pointing aids make keyboard easier to use. The mobile arm supports prop the arm while the pointer helps people who cannot isolate and extend a finger in order to press a key. In addition to control enhancing devices, strategies such as changing the position of the control interface is also a control enhancer. Making a slight change to the angle or height of a control interface may make it easier for the client to activate.
Discuss the effort, displacement and deactivation characteristics of a control interface
Effort - Refers to the amount of energy a user must expend to activate a control interface. For mechanical interfaces, effort is measured by the amount of force required to activate the switch. For electromagnet interfaces, it is the minimum amount of movement required for activation. With respiration control interfaces, different levels of effort activate different responses. For example, a hard puff might send a wheelchair forward while small puff turns it to the right. Displacement - Refers to the distance between a mechanical control interface in its original position versus the control interface when it is activated. Some interfaces, such as force-activated joysticks, require no displacement. Other interfaces, such as switches and keyboard require displacement. Deactivation - Refers to the force needed to deactivate a control interface. For mechanical interfaces, it usually takes 1/3 to 1/2 less force to deactivate a control than to activate it.
Discuss the skills required to use an eye-controlled communication system and the limitations of such a system
Eye-controlled communication systems are good choices for people with limited speech abilities and with little to no movement in their limbs: for example. someone with high-level quadriplegia or who has had a brainstem stroke. People using either type of eye-controlled communication system must have good vision and control in at least one eye. They must also have good head control and be able to keep the head relatively stationary. In addition, they must have the cognitive ability to follow instructions. Eye-controlled communication systems are expensive compared to other input methods. In addition, bright lighting, whether sunlight or indoor lighting, sometimes interferes with eye-controlled communication systems. Contact lenses may also interfere with the tracking process.
Discuss the flexibility, durability and maintainability characteristics of a control interface
Flexibility - Refers to the number of ways a control interface may be operated. Control interfaces that are activated by movement are typically more flexible than mechanical control interfaces because the movement interfaces are activated at several body sites. Also refers to the ways in which a control interface may be mounted. Durability - Refers to how well an interface will hold up to its intended use. An interface that will be used a great deal and subjected to force and pressure needs to be made of durable, long-lasting materials. Maintainability - Refers to how easy the control interface is to clean, repair, replace and keep in working order.
Compare and contrast integrated distributed control
Integrated control means that several applications or devices use the same control interface. Integrated controls keeps the user from being surrounded by multiple controls. Preferable when the user has only one reliable control site; the best control interface for each device is the same; the single interface is easy to use; or the user prefers integrated controls. Distributed control means that each device has its own separate control interface. Preferable when an AT device doesn't perform as well with integrated controls; the user wants to use an AT device away from his/her powered wheelchair; visual, cognitive or visual/perceptual limitations require separate controls; the user prefers separate controls; or integrated controls cost too much or are technically impossible.
Discuss methods of activation for a control interface
Method of activation refers to they way a signal sent by the user activates the processor. Common methods of activation are movement, respiration and phonation. The control interface detects movements through mechanical control interfaces, electromagnetic interfaces, electrical control interfaces, or proximity control interfaces. Switches, keyboards, joysticks, computer mouses and trackballs are all examples of mechanical control interfaces. Electromagnet interfaces use light or radio frequency to detect movement from a distance. Head-mounted light sources are an example of this type of control interface. Electrical control interfaces react to electrical currents. Examples are electrodes connected to the skin. Proximity control interfaces react to heat such as body heat. Electrical and proximity interfaces do not require bodily contact. Respiration may be used to activate an interface through airflow or air pressure. The user must be able to place his/her lips on a tube and keep them there while producing controlled airflow. Phonation refers to sounds produced by airflow.
Define momentary control. latched control, tremor dampening, and short throw adjustment
Momentary control - Controllers activate motors only when the switch is pressed, providing the greatest user control Latched control - Controllers turn the motor on the first time a switch is pressed and turn it off the next time the switch is pressed. This type of controller is helpful for users who can press and release a switch quickly but who cannot hold the switch in. Tremor- or sensitivity-dampening - Controllers ignore small, rapid movements and respond only to large, slow movements. This feature is useful for people who have difficulty controlling their movement because of tremors. Unfortunately, it also makes it more difficult to respond quickly to obstacles. Short throw adjustment - changes degree of range of motion a user needs to operate a control interface.
Discuss the use of trainable or programmable controllers
Remote devices using ultrasound, infrared or radio frequency waves typically control only one device. If the consumer uses remotes with several appliances, "controller clutter" does sometime occur. Trainable controllers are designed to eliminate this problem because they may be adapted to work with any appliance. Codes for a variety of appliances often come preprogrammed into the trainable remote device or the consumer can train the new controller by pointing it at each individual controller and pressing the function to be stored. Programmable controllers are similar to trainable controllers except that the consumer physically enters the code into the controller, using a table of codes provided by manufacturers. Standard home electronics remotes may be used as controllers for consumers who can press the buttons on these remotes. Other units are available with expanded keyboard, scanning access and other direct and indirect selection methods.
Discuss the spatial characteristics of a control interface
Spatial characteristics of a control interface refer to its physical size, shape, weight, number of targets and amount of space between targets. Different types of levels of skill are best suited to specific special characteristics. For example, a single switch has one target. This interface is best suited for a person with limited range and gross resolution. A person with more refined resolution might be able to use a joystick, which has two to five switches. Someone with fine resolution can use a keyboard, which has from two to 100 targets. However, the size of the keyboard depends on the user's range. Contracted keyboards are best for people with small range, standard keyboards require moderate range and expanded keyboards require large range.
Discuss the control interface element of the human/technology interface
The control interface is the actual hardware a person uses to control an AT device. It may also be called an input device. A keyboard and a joystick are both examples of control interfaces. The signals that a control interface generates are called the input domain. It may be discrete or continuous. If a control interface has discrete inputs, the size of the input domain is the same as the number of targets the user can choose from. For example, a keyboard in which each key represents a specific letter, number or symbol is discrete. If the control interface has a continuous input interface, the inputs have an infinite number of values. A joystick, computer mouse and volume control knob are all examples of a continuous interface.
Compare and contrast the types of eye-controlled systems available as control interfaces for direct selection
The first eye-controlled communication systems were manual, with users communicating through eye blinks or using their eyes to point to letters on an alphabet board. Two types of electronic eye-controlled system are also available. Both give the user computer access, environmental control and telephone operation. The first kind uses infrared video camera mounted below a computer monitor. The camera shines a beam into the user's eyes to determine what the user is looking at. The user makes a selection by looking at an element for a specified time. The other type of electronic system tracks eye movement through a viewer mounted to a standard pair of eyeglasses. The eye movements are then translated into keyboard input.
Discuss the sesory characteristics of a control interface
The sensory characteristics of a control interface refers to its auditory, somatosensory and visual feedback. A keyboard that clicks when the user presses a key is giving the user auditory feedback, while texture of activation surface provides somatosensory feedback. Treads, wobbles, and rockers provide all three types of feedback: audible clicks, visual movement and tactile sensations. In general, the more force a control interface requires for activation the more feedback that interface offers. Interfaces that offer sensory feedback generally help users perform. However, if the feedback startles or distracts the user, the ATP may need to consider other control interfaces or ways to adjust the feedback.
Discuss how the ATP applies knowledge from the needs identification and physical-sensory evaluations when selecting a control interface
Through the needs identification evaluation, the ATP learns what the client needs and wants to do. The ATP then determines how many activities need to be performed, how many input signals each activity will require and whether one control interface will be enough for all needed activities or more than one control interface is needed. The physical/sensory evaluation tells the ATP what skills the client brings to the activity. Through this evaluation, the ATP can determine the client's sensory needs, functional range of motion, resolution skills and possible control enhancers. The ATP can also identify potential anatomical control sites. With all this information, the ATP can determine whether to select control interface with direct or indirect inputs. He or she may then select potential interface for comparative testing.
Discuss the use of touch screens and Tongue Touch Keypads as control interfaces
Touch screens allow the user to point directly to a selection set on a screen with a finger or a pointing device. Touch screens are especially good for children because they provide a direct, intuitive way to make a selection. Tongue Touch Keypads consist of a dental mouthpiece that fits int he roof of the mouth. The mouthpiece has up to nine small switches the user activated with his/her tongue. The mouthpiece then sends infrared signals to the computer. These keypads are useful for clients who have limited motor control in their limbs but have good head, neck. and oral motor control.
