First of all, it should be said that automatic writing has never been part of the mystical tradition of our Church. Many people believe St. Catherine of Siena used a form of automatic writing because of the fact that she did not know how to write and yet received many messages from the Lord which she was able to record. However, St. Catherine actually received the gift to write as if she had always known it and did not participate in any form of guided writing. � "Mystics have always been respected in their humanity and their liberty, and have never been guided by God against their will and forced to do things that they could not achieve otherwise," says Father François-Marie Dermine in an interview regarding his critique of the writings of Vassula Ryden.
A Catholic mystic can never be in the same category as a medium - which is essentially what a person becomes when participating in automatic writing. When a saint writes what God inspires him or her to write, the person is always fully aware of what they're writing and are not allowing themselves to be used as a kind of channel, which is the case with automatic writing. As this blog explains, automatic writing is also known as trance writing because the recipient goes into a trance and allows a spiritual entity to dictate whatever message it wishes to convey. This is a form of mediumship, or channeling, which allows a spirit to temporarily possess a person.
At no time does God behave in such a way with His saints. While mystics are known to go into states of ecstasy, God does not "possess" their bodies and use them to do His bidding. He always respects the free will of His creatures.
As for the kind of locutions Christians experience, these can occur in several different forms.
Corporeal locutions are those actually heard by the physical power of hearing, which are very rare and, therefore, highly suspect. The devil is more than capable of speaking to us and can fool even the most adept soul. The saints, such as St. Teresa of Avila, a Doctor of the Church, recommend that we ignore these messages entirely.
Imaginary locutions are those referring to the imaginative faculty which receives the same kind of impression it would have received had it heard words.
Intellectual locutions are considered the most reliable. In this type, God imprints what He is about to say in the depth of the spirit, without the use of a voice or sounds. It is often described as an "infusion of knowledge," or a sudden clear understanding of some subject or situation.
But receiving these locutions doesn't occur in a vacuum. They are most commonly found in the lives of people who are deeply committed to the Gospel of Jesus Christ and who are genuinely seeking communion with God.
However, this isn't to say that every locution heard is clear and authentic. We have a fallen nature and because of our frailty, will not receive every revelation perfectly from the Holy Spirit.
For further reading on this subject, see Father Benedict Groeschel's book, A Still Small Voice, which I would recommend to anyone reading this blog.