In my previous post Is predictability incompatible with responsibility for sin? I argued that there is a difference between predictability or determination to evil and to good; since the will's first inclination is to good, a determination to or predictability of evil that comes from without (e.g., due to circumstances, etc.,) diminishes the freedom and responsibility of an act, while a determination to good need not. Another way to illustrate the same point is in terms of the classical teaching on ignorance as a cause that makes acts involuntary.
Suppose there are two persons with basically the same degree of virtue, each faced with a similar choice between a good and necessary act and an evil act, and that in normal circumstances each would be fairly likely to choose the good act. Now suppose that the first person is going to be so convincingly persuaded (by the devil, by another person, or by circumstances) to do the evil act that there is no significant possibility that he will not do it, while the other person is going to be so convincingly persuaded to do the good and necessary act that there is no significant possibility that he will not do it. In the first instance, the person acts on account of an error that is put upon him from without, while in the second case, the person acts on account of a true insight and/or opinion concerning the value and necessity of the good act. Hence the first person's act is involuntary insofar as it proceeds from an error for which he is not responsible (unless there were grave neglect involved in the process of being overwhelmed by the error), while the second person's act is voluntary.
In Aquinas's account, leaving aside the causality of original sin, the influence of other persons (human beings or the devil) reduces to making someone perceive things in a particular way, either by presenting them with an argument, concept, idea, picture, etc., or by affecting their emotions, which makes them perceive things in a particular way. This seems to imply that given someone is faced with a specific choice, temptations from without, to the extent they increase his probability of making a wrong choice, decrease the voluntariness of that choice, unless and to the degree that there is neglect involved in letting himself be affected by the temptation.