As Sankha has mentioned, the determining (votthapana) citta is functional (kiriya); it is not the result of kamma, nor does it create kamma. This is an important point, because if the reaction to an object was fixed according to kamma, then there could be no spiritual development (everything would be predetermined).
There is no "self" who decides how to react, the reaction arises naturally due to conditions. For example, consider the last time that you were confused about something... was there a conscious decision, "I think that I will choose to be confused now!" Of course not, confusion arose naturally. Just as confusion arises naturally, other reactions arise naturally as well.
From an Abhidhamma perspective, the primary conditions that influence the votthapana citta and determine the nature of the subsequent javana cittas are object-predominance-condition (arammanadhipati-paccaya) and natural-decisive-support-condition (pakatupanissaya-paccaya).
In simple English, object-predominance-condition means that some objects are naturally going to elicit a strong reaction of a certain type. Natural-decisive-support-condition means that "past strong" experiences naturally condition a reaction.
Let's look at the natural-decisive-support-condition in a bit more detail. If I have a daily routine that involves metta meditation, this repetition creates "past strong" experiences that will cause the mind to naturally react with metta when facing a new situation. If I had a really bad day at work, these "past strong" experiences may cause the mind to naturally react negatively when I get home. If I had a traumatic experience of drowning (or almost drowning) in my past life, this "past strong" experiences may cause the mind to naturally react with fear when in a boat.
Natural-decisive-support-condition explains that the mind cannot be controlled, but it can be trained (just as a puppy dog cannot be controlled, but it can be trained). If you want to develop yourself spiritually, train the mind through repetition and make the training stick through strong volition.
When we approach our spiritual development as a gradual training exercise, we then know that it requires lots of energy, lots of repetition, lots of patience and that it takes time.
If you want to train yourself to play the piano well, you can’t spend just a few minutes on it from time to time. You have to commit to regular practice, energy, repetition, patience and time. The training associated with spiritual development requires a similar commitment, but the rewards are much greater than becoming a skilled pianist.
The literal translation of the precepts are "rules of training". Think about the implications of this.