Communication capabilities range widely among people with IDD, who include those with cerebral palsy and Down syndrome. Some find it difficult to speak but are able to read, while many can communicate easily in person but struggle to read, according to Margaret Nygren, the executive director and chief executive of the American Association on Intellectual and Developmental Disabilities, or AAIDD.

“It’s a lot easier, and fairly enough, for web developers and the tech community to focus on a one-off, one-size-fits-all solution for, say, people who are blind or low vision, rather than provide accommodations for a group of people who are on a continuum,” said Dr. Nygren.

For Peter Berns, CEO of the Arc, a charity that promotes the rights of people with IDD, accommodating “cognitive disability is, in a sense, the final frontier of accessibility.”

Some organizations are trying to make the web more accessible for people with IDD and learning disabilities.

LAB Group Services Ltd., a collective of digital marketing agencies based in London, is building software that could help companies detect whether a user interacts with a webpage in ways that might indicate neurodiversity or cognitive vulnerability, such as frequent scrolling up and down the page, filling in form fields out of the usual order and higher use of the back and forward buttons on a browser.

The agency’s Intra-Browser Vulnerability Assessment, which was originally designed with the personal banking sector in mind, can then prompt websites to display information in a much clearer way on subsequent pages, according to LAB Group. The company in March received a government-backed grant to develop the technology, and aims to introduce a commercial product in May 2021.

“A single online transaction path must be tuned for the majority,” said Adrian Webb, chairman of LAB Group. “Multiple paths can be individually tuned to more diverse needs.”

Alternative systems are particularly important for online job applications, said Mark Capper, the head of development at Mencap, a charity that aims to improve the lives of people with a learning disability. A number of people with IDD and learning disabilities struggle to submit applications because website timers often log them out before they have time to complete their forms, Mr. Capper said.

Mencap’s own job application form includes a simple PDF version that can be completed and emailed, or printed out, filled in by hand and mailed to the company. The PDF reduces the cognitive load that comes with processes like creating an online profile and remembering a password for online forms, Mr. Capper said.

Each field on the PDF is illustrated with a relevant photo. For example, the field requesting “Your address” is accompanied by an image of someone writing on an envelope.

The Mencap form is also written in “plain language,” a term used by accessibility advocates to refer to writing that avoids long words and complicated sentences and defines terms like “equal opportunity employer.”

“Plain language cuts through where stylistic choices may obscure meaning,” said Rebecca Monteleone, an assistant professor of disability studies at Ohio’s University of Toledo.

Dr. Monteleone worked with news publisher ProPublica to create its first plain-language translation of a story, published in November. The article covered the failings of Arizona’s IDD services, and therefore warranted a version that could be read by some people with IDD, said Arizona Daily Star reporter Amy Silverman, who wrote the article as part of an investigative series sponsored by ProPublica’s Local Reporting Network.

Creating a plain-language version of the article was a slow process: Dr. Monteleone had to reorganize paragraphs, simplify the article’s language and sentence structure, and add explanations of certain words and concepts where necessary. The context and empathy required to translate text into plain language makes automating the process difficult or impossible, Dr. Monteleone said.

Companies must decide whether providing plain-language versions of their text is an appropriate use of their resources, said the AAIDD’s Dr. Nygren, who noted many people with IDD cannot read. Her organization has chosen to present the findings of its academic research in the format of a more accessible cartoon rather than a plain-language version.

Liz Weintraub, senior advocacy specialist at the Association of University Centers on Disabilities, says plain-language versions make accessible stories or articles she might otherwise have been excluded from.

“If the conversation is too hard for me and my friends to understand, then how can we contribute to it?” said Ms. Weintraub, who was born with cerebral palsy and an intellectual disability.

Write to Katie Deighton at [email protected]