What study showed that humans can successfully detect objects within images once they are able to recognize those objects? A professor in an online lecture I was watching referenced a study which he said showed that our ability as humans to detect objects within scenes (especially complex scenes) was very much connected with our familiarity to the objects in the scene.

In particular, one of the images in the study was this one:


He said that the study reported that if the subjects had never seen a dalmation before then they often failed to segment the picture accurately.
Using Google's search by image feature, I found that the image is usually entitled Richard Gregory dalmatian.

From there, I found this page, which cites the image as coming from Gregory's 1970 book The Intelligent Eye. There's also, incidentally, a good list of Gregory's publications on this personal web page, which is probably worth looking at.

From a theoretical perspective, the image is a demonstration of the role of top-down expectations in perception - we see not what's there, but a combination of the input to our retinas and what our prior knowledge tells us should be there. This is a case of Bayesian perception, and can be read up on in Kersten et al (2004), amongst many other places.