Organically sensitive is not a phrase you'll find anywhere, but it refers to people who have been Sensers since early childhood, so that it has become woven into their physiology - as opposed to those who have developed their sensitivity later in life.
Looking where organically sensitive comes from, there is a window of time where it peaks. If we were to make a graph with time on one axis and susceptibility to this piece that lets you be organically sensitive, there is a short series of peaks, with the largest one around age nine. Your system becomes hyper aware to what you are holding at this time, and by holding Senser through that time, you are likely to become organically sensitive. It's a systemic vulnerability to being tuned to a particular specialty, and as such those are the times where paying extra attention and encouraging children to hold what they want may make their lives much easier.
(This may not just apply to humans, but also to other species)
Angel, 2015-03-31