I don't believe I'm in full agreement with either Gazza or Shooter.
Taijiquan, when trained for its Martial application properly, will defend you without thought. The body reacts on its own.
Should you speed up your practice? no
One thing that the chinese used for reaction conditioning, was repetition. Continuous practicing of the same form, over and over.
Visualization is the key. Once you know the form, then the visualization may begin. Seeing opponents on either side of you is the key to the conditioning of your reaction time. But still, do you speed up? no, theres no need. What you want to do is imprint the scenario into your mind, see yourself counter-attacking with your form. So when the scenario presents itself in a real life situation, you dont think, you react.
I have trained in such a way for a long time now. I have also used the art in real life situations. If anyone needs me to clarify, then just ask and I will try to further my detail.
-Mike
"If you do not wish to grasp the thorn, you should not crave the rose."