This is the study the following paragraphs refer to.

Memory researchers in the 1960s subjected college students to one of the most terrifyingly-named memory tests ever invented: the Two-Alternative Forced-Choice Test. In it, college students were shown 612 magazine ads (possibly tied to chairs with their eyes held open) and then asked to identify the old pictures when shown a new mixture of images. The students correctly picked the old images 98.5 percent of the time.

Unsatisfied, the researchers repeated their tests with more images, trying to determine what college students will put up with for low pay and free food. There doesn’t seem to be a limit. Students were willing to sit in dark rooms for five consecutive days, watching ten thousand images in a row. After the study, these students accurately identified 83 percent of the images.

Our capacity for visual memory is extraordinary; we only need to learn how to take advantage of it. Since we need to learn words, not pictures, we will use combinations of words and pictures. Such combinations work even better than pictures alone. This effect even applies to totally unrelated images: you will remember an abstract drawing with the sentence “Apples are delicious” better than that drawing alone.