[mudita]

You slightly misremembered the invisible gorilla test, a classical study about inattentional blindness.

https://en.m.wikipedia.org/wiki/Inattentional_blindness#Invi...

Somewhat fittingly "the basic Simons and Chabris study was reused on British television as a public safety advert designed to point out the potential dangers to cyclists caused by inattentional blindness in motorists."

[Lio]

I beleive that the paper was originally titled "Gorillas In Our Midst" which is a wonderful play on the title of the Dian Fossey book Gorillas in the Mist.