Psychological problems include extreme anxiety, redirected aggression, fear and several other potential problems. If a cause can be identified, either physical or psychological it is easier to predict whether or not treatment will be beneficial and obviously easier to choose the treatment plan most likely to work. Good luck with this. I wish I could give you a more specific answer but this is another one of those problems that requires an examination and detailed history taking. Ankle biting and sudden attacks are most often associated with predatory aggression.
Cats have a strong natural desire to hunt.
Inside the house, there isn't much to satisfy this desire. In some cases it is possible to provide a more appropriate toy to satisfy the predatory urge. Some people just tie a toy on a string to their belt to provide a better target then their ankles. This also provides a lot of exercise which is a good release of the pent up energy in many kittens. Most cats will outgrow this behavior by the time they are a couple of years old and are much better if given alternatives objects to attack and sufficient exercise. .