How strong can a groinal response be? Is this one?

First, I'd like to recommend you to read this (but it's a lot to read, do it only if you want): http://www.nofap.com/forum/index.php?th ... elp.26885/

Can the penis get as hard as when you're aroused? Can this happen before you have problems with anxiety?
Right now, because of HCOD, everything is messy. But I remember that mine would get hard if I saw some "typical porn star's penis", even if I didn't feel aroused by it, unlike girls. Happens more with pictures or solo videos, before HOCD I was sure gay porn never did it for me (although now I can't say anything because everything is messy because of the HOCD) Also noticed that I don't usually get 100% hard without the help of my hand, but remember in one of the first tests I did that I didn't need the hand.

After HOCD slowly hit in, I remember not being able to tell if my brain was aroused or not in these situations. But before it did, I don't remember ever getting in the mood from that, but my friend down there...

Do you think this maybe because:
1) I'm 16 years old and have been watching a lot of porn since 8, so my brain associate one thing with another?
2) pure groinal reponse?
3) other???

This is pretty much what started my HOCD. Now, of course, it has got as deep as hell and I had every single symptom (don't feeling them right now, though).

Att 1: just made a test... While thinking about a very specific penis I got hard without hand. Then went to a site of naked men pictures and didn't get hard even with hand, then went to a site of straight pictures and also couldn't get hard...

Maybe you associate a man's genitals with your own genitals and your own arousal?

EDIT: And when you watch porn it's very likely that you're aroused because a) it's sexual and anything sexual can be arousing and b) porn is made to turn people on.