Today's Google doodle might look familiar to anyone who's ever waited on a subway platform in New York. The design is an homage to the late Seiichi Miyake, the inventor of the Tenji block (also known as the braille block), which is a ubiquitous, critical presence at subway stations and sidewalks around the city.

Also known as a tactile paving slab, the Tenji block is a guidepost for blind and visually impaired residents. Each block has a series of elevated bumps and ridges which denote different cues. On the sidewalk there are bars suggesting direction, such as a cue to go forward, which are placed where one crosses the street, as 99 Percent Invisible reports. On New York City subway platforms they are placed at the edge before the track and on stairways, with raised dots indicating "STOP." These can be felt through shoes, or with a cane.

“The installation of Miyake’s Tenji blocks in Okayama 52 years ago today is an important benchmark in disability rights," Marc Fliedner, Program Director of Disability Rights New York, tells Gothamist. "Miyake recognized the need for people who are blind and sight impaired to safely navigate urban streets in order for them to have full and equal access to all that a city has to offer."

Miyake invented the Tenji block in 1965, and it was first installed on this day in 1967, near a school for the blind in Okayama, Japan, as CNET reports. The blocks spread across Japan, first to railway stations and then to government buildings, throughout the 1970s and 1980s, and other countries around the world following suit.

Fliedner says that the United States began installing tactile walking surface indicators at subway platforms in the early 1990s, as part of ADA Accessibility legislation. In 2001, the blocks started appearing at sidewalk curb cuts. Tenji blocks—yellow on subway platforms, and grey on sidewalks—have become an integral part of New York City over the past two decades. (The MTA did not immediately respond to a request for comment.)

While these blocks have been invaluable to help blind and visually impaired pedestrians get around, it can prove to be challenging for people with other disabilities—the dots and ridges can be challenging for someone on crutches to navigate, for instance. They have a ways to go with being completely ADA accessible, too: The Red Hook Star-Revue notes that a 2014 canvassing project helmed by Manhattan Borough President Gale Brewer and her team found that of 1,209 sidewalk curb cuts, only 115 bore the correct "truncated domes" making them accessible. "Of course, anniversaries also highlight how long smart ideas take to become a reality," Fliedner adds. "Fifty-two years is a long time, and it is still a struggle to get and maintain the tactile walking surface indicators at all appropriate city locations. Disability Rights New York will continue to advocate strongly for compliance with the Accessibility Guidelines until the full and equal access Miyake envisioned is fully realized."