Erotic Literature

As we all know, science is slowly catching up in studying the effects of porn on humans.
There are various studies linking porn consumption to less willpower, less grey matter in the brain and all of those other negative effects.
But all of these studies only considered visual pornography.

So my question is what are the effects of erotic literature compared to visual pornography?

Anyone, who has read 50 shades of grey, says it´s basically porn for women (I haven´t, I only know this from second hand). And if you look at amazon, the best selling book are so called "romance" novels. I am sure most people on there would consider these books pornographic, yet it is even more accepted in our culture to read these books than look at visual pornography.

Feel free to post any experiences you have with this subject, be it first hand or from other people.