From Azuma Hiroki’s Otaku: Japan’s Database Animals:
Many of the otaku today who consume adult comics and “girl games” probably separate [genital needs and subjective “sexuality”]; and their genitals simply and animalistically grew accustomed to being stimulated by perverted images. Since they were teenagers, they had been exposed to innumerable otaku sexual expressions: at some point, they were trained to sexually stimulated by looking at illustrations of girls, cat ears, and maid outfits. However, anyone can grasp that kind of stimulation if they are similarly trained, since it is essentially a matter of nerves. (89)
Recent pictures of AKB48 (scroll down).