As machine learning and the use of artificial intelligence spread, technologists are running into questions over when A.I. can get too real — and too creepy.

One area where that is increasingly cropping up is in speech that is powered by technology, John Markoff writes. As voice-controlled digital assistants like Siri, from Apple, and Alexa, from Amazon, are being embedded in devices like the iPhone and the Echo speaker, software designers are paying attention to speech and how to cross the “uncanny valley,” the point at which the technology becomes too creepy and weird.

The phrase “uncanny valley” was coined in 1970 by the Japanese roboticist Masahiro Mori. It’s a phenomenon bedeviling more technologists these days, as machine learning start-ups sprout and giant tech companies including Google and Facebook dive headlong into A.I. It can play into our worst fears about artificial intelligence — here’s a list of creepy uncanny valley moments — and has even spawned a futuristic play.