Mark Williamson wrote:
Now, that aside, there's another major problem: accent. Who's to say I could understand what you were saying, if you said "star"? There is no unambiguous way to represent words through audio.
That's a theoretical possible problem rather than actual data (which is why that' s what I asked for) or even anecdote.
I haven't found data yet, but here's a page of theory with anecdote:
http://www.standards-schmandards.com/index.php?2005/01/01/11-captcha
Note they get around your problem by using numbers. This apparently worked on three casual test subjects. Though that, of course, is anecdote, not data.
The W3 paper just provides possible approaches with no words on effectiveness: http://www.w3.org/TR/turingtest/
Evidently the audio option was frequently unusable a couple of years ago: http://news.com.com/2100-1032-1022814.html - I would *presume* there's been improvement since then.
Does anyone have or know of *actual data* (rather than hypothesis or anecdote) on whether non-visual captchas are any good as yet?
- d.