1. Perceivable

Introduction to Perceivable

Principle 1: Perceivable

Information and user interface components must be presentable to users in ways they can perceive.


Perceive: 1. To become aware of (something) through the senses, especially the sight; recognize or observe. 2. To come to comprehend; grasp (dictionary.com)

The Principle Explained


As suggested in the first definition above, people must be able to perceive web content through one or more of their senses. When a person cannot see or hear, for instance, and an alternate means of perceiving is not available, then that content becomes inaccessible to them.

Content may not be perceivable if web authors:

  • choose small or hard-to-read fonts;
  • specify colours for fonts that do not provide sufficient contrast with the background;
  • leave out a text description of a photograph;
  • do not provide captions or a transcription for multimedia and audio content; or
  • require timed responses.

Perceptual barriers occur when information is communicated entirely through one of the following:

  • Sight
  • Sound

Most people perceive web content through sight and sound. When content is communicated exclusively through one sense, such as sight, some people will not be able to perceive it.

These types of perceptual barriers are addressed through Guidelines 1.1, 1.2, and 1.4.


The second definition suggests people must be able to comprehend or grasp web content. The ability to comprehend web content can be affected by the structure, the relationships between elements, its complexity, or consistency in the presentation.

Perceptual barriers of this nature occur when:

  • information is poorly structured;
  • navigation or presentation is inconsistent;
  • the focus ordering of content is illogical;
  • functional elements are not effectively described or labelled;
  • content operates only in a single display orientation; or
  • instructions reference content solely through shape, colour, size, or visual location.

These types of perceptual barriers are addressed by Success Criterion 1.3.3 (sensory characteristics), described later in this unit.

Suggested Reading: WCAG 2.1 Perceivable


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Introduction to Web Accessibility Copyright © 2019 by The Chang School, Toronto Metropolitan University is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.

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