The WCAG principle of Perceivable ensures that information and user interface components are presented in ways that everyone can detect and interpret, whether visually, audibly, or through assistive technologies. Barriers to perceiving your content might not even be permanent, they could be temporary, but your learners need to be able to access your content regardless.
This is not just a technical requirement; it determines whether the design holds once ideal conditions do not. Imagine trying to watch a video on how to complete an assessment on a packed train as you commute home from work. Are you confident you know what you need to do?
If your course isn’t perceivable, learners may well be trying to complete it without being able to see or hear the content. For learning designers, this principle is where we can make the most immediate and meaningful impact.
What Does Perceivable Mean?
Perceivable content is content that can be experienced through at least one sense. For example:
- A learner who cannot see an image should be able to understand its meaning through alternative text.
- A learner who cannot hear audio should have access to captions or transcripts.
- A learner with low vision should be able to read text with sufficient colour contrast or magnification.
WCAG breaks this principle down into specific success criteria, many of which fall squarely within the learning designer’s control and don’t just impact learners with differing sensory abilities. Most of these criteria will affect most learners at some point. Poor internet connection and the image doesn’t load? Read the alternative text. In a library and forgot your headphones? Read the captions.
This is why perceivability functions as a test of whether a design only works under ideal assumptions, but they can also simply aid learning for being present as opposed to absent. Want to grab a quote but can’t remember where it is in a video? Ctrl F the transcript. Studying in a second language? Read the captions as you listen. (For more on building clear, cognitively accessible content, see WCAG Understandable.)
Making content perceivable is good learning design.
Key Actions for Learning Designers
Here’s what you can do to make content perceivable:
Provide Alt Text for Images
Every meaningful image, including those in quizzes or other interactive content, needs alternative text that describes its purpose or content. This is essential for learners using screen readers. Avoid vague descriptions like “image” or “graphic”, instead, convey the image’s function in context. For decorative images, mark them as decorative so they’re skipped by assistive technology.
Tools like Articulate Storyline 360 and Blackboard Ally now offer AI-suggested alt text, which is a good start, but you’ll need to review and refine for accuracy, particularly for more complex images. Both Microsoft 365 and Adobe Acrobat have accessibility checkers that are fairly easy to use though both will assume descriptive text is needed for all images when it might not be. I found that existing guidance didn’t go into the depth that I was needing on a regular basis, so I created my own decision tree. Use it to guide your choices if and when you aren’t sure when to include image descriptions.
Add Captions and Transcripts
Videos and audio files should include captions for spoken content and transcripts for full accessibility. Many platforms, including Microsoft Stream and YouTube, offer automated captioning though these should always be checked for accuracy as they often misinterpret technical jargon. Creating transcripts for third-party videos without permission breaches UK copyright law. When transcripts are poor or missing, I provide text-based alternatives that cover the same information. This also benefits learners who have limited digital access or simply prefer reading and proved effective in a nursing course, where many learners preferred reading over video. As the example above shows, though captions and transcripts we included to make content accessible to those with hearing loss, they are beneficial for many others for a variety of reasons. (If you’re considering multimedia structure more broadly, see Top Multimedia Principles for eLearning Design.)
Ensure Sufficient Colour Contrast
We have all squinted at images and text which aren’t clear and for some this is more of a problem than for others. For WCAG compliance, text and background colours must meet specific contrast ratios to remain readable for learners with low vision or colour blindness. For reference, normal text requires a 4.5:1 contrast ratio while large text needs 3:1.
Avoid using colour alone to convey meaning, like with “click the red button”. Instead, pair colour with text or icons or even patterns.
I like WebAIM Contrast Checker to help verify compliance but there are other built-in browser extensions that you might like better.
Offer Flexible Formats
Consider providing content in multiple formats like text, audio, and video so learners can choose what works best for them rather than relying on a single pathway that may not hold under real conditions. For example, providing a text-based alternative for information in a YouTube video as mentioned above or providing downloadable PDFs in video-heavy modules to help learners in low-bandwidth areas. This aligns with Universal Design for Learning (UDL) principles and supports diverse learning preferences. (If you want to explore how collaborative tools influence access and equity, see Collaborative Tools for Enhanced Learning.)
Why Perceivable Matters
There are a variety of browser extensions that allow you as a learning designer to experience your content through the eyes of those with accessibility needs. These should make it clear why perceivability matters. It is the first step toward digital accessibility and inclusive learning design. By adding alt text, captions, transcripts, and ensuring colour contrast, you remove barriers that prevent learners from engaging fully.
For learning designers, this principle is a practical, cost-effective starting point for embedding accessibility into every project that can have the most immediate effect on learner engagement and outcomes. Start small: audit your next course for perceivability. Check alt text, captions, and colour contrast. These simple steps can improve engagement and success rates, but more importantly, reveal whether the design is robust when learner variability is taken seriously.
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