Georgia Tech Research Institute
 
Accessibility Assistant

Accessibility Assistant

Issues

Pointing Devices: Issue 2 of 5

Issue: Using pointing devices can be difficult for users with upper mobility impairments.

Three on-screen buttons (history, culture, and science) are shown, and the user is using a stylus to select the history option.  The controls are very small and closely spaced, and therefore require the user to be very precise when making a selection.

Devices such as mice, track balls, touch pads, and styluses require users to make small, controlled, and precise movements. Users who lack fine motor control may have difficulty stabilizing their movements to provide accurate input with a pointing device. As a result, they may have difficulty performing the desired actions, and may also activate controls unintentionally.

Populations Impacted: Users with upper mobility impairments.

Potential Solutions:
  • Ensure that on-screen controls are large and are spaced far enough apart to minimize accidental activation of adjacent controls. The active area of on-screen controls should be large enough to provide a margin of error for successful user inputs. For example, according to the Human Factors Design Standard (HFDS), touchscreen buttons should be between 0.75" and 1.5" along each side, with spacing between buttons of 0.13" to 0.25". This will help ensure that a user who does not have fine motor control is able to activate a button without accidentally activating adjacent controls.

  • Three on-screen buttons (history, culture, and science) are shown, and the user is using a stylus to select the history option.  The controls are large and widely spaced, and therefore require relatively little precision when making a selection.
  • Ensure that the gain for free-moving cursor control is set appropriately. If the gain is too high, small movements of the input device will result in large movements of the on-screen pointer, which causes problems for users lacking fine motor control. A non-linear gain curve, which results in very small cursor movements in response to small movements of the input device, with the rate of movement increasing for larger movements of the input device, can accommodate the needs of both users lacking fine motor control and users without motor impairments.

  • Provide an alternate display mode with larger, more widely spaced controls. If the normal display cannot be made accessible, providing an alternate display mode with larger, more widely spaced controls, even if it contains only the most frequently used controls, will be useful for users who lack fine motor control. If the user interacts with the display via a free-moving cursor, lowering the gain when the alternate display mode is active may make it easier for users to interact with the display.

  • Provide an alternative interface that does not require the use of a pointing device. For example, a set of hardware controls that allows users to use arrow keys to move a highlight cursor among the various on-screen controls, and provides a button for selection of the highlighted item may be easier for users lacking fine motor control to interact with than a pointing device.

  • Provide a clear area around the pointing device for users to brace their hands. For pointing devices such as track balls and touch pads, providing clear space around the pointing device where users can brace their hands to steady themselves and reduce tremors can help users perform actions more accurately.

  • Provide visual and auditory feedback when user input is received. Providing visual and auditory feedback when user input is received can make up for the lack of tactile feedback from on-screen controls, and helps users detect unintentional activations. Visual feedback can be provided in the form of salient visual changes in the display. Audible feedback might consist of simple tones, or speech output when more descriptive feedback is needed.

  • Allow easy recovery from errors. A "Back" or "Undo" button should be provided to allow users to recover from accidental inputs. Note that a button labeled "Cancel" is somewhat ambiguous; a user may think that a "Cancel" button will cancel the entire transaction, rather than cancel only the most recent input.

Applicable Guidelines:
ADA-ABA - 707.5
Section 508 - 1194.31(f)
HFDS - 6.4.1.1, 6.4.1.9, 8.1.2.9, 8.15.11.1.13, 8.15.11.1.14