What kind of psychological processes can be said to be involved in procrastination?

Perfectionism: can be associated w/procrastination. If we can't do things good enough then we wait until the last minute and use it as an excuse. Work at accepting yourself and this imperfect world and doing what you can. A sage once said "Perfection consists in working against your imperfection." That's all it takes. Peace and good health.

Avoidance : Avoidance behavior is important to consider. We tend to avoid behavior and activities that make cause discomfort or distress (anxiety or fear). This may happen when we lack self-efficacy (confidence and skills) to manage a behavior or situation. Interestingly avoidance can be self-reinforcing - the more one avoids, the stronger the anxiety for avoidance becomes, making it harder to get started.

Good answers!: The Docs gave interesting, good answers for psychological basis of that issue. There may be others like OCD, depression, etc too. If you're writing a paper it will help. If you suffer this - you'll need more. Brief therapy can be useful - there are good books like The Willpower Instinct - by Kelly McGonigal. There are many - sample online. Just do it! :-)