Repeat exercise #4, but do it while also imagining the feeling of the material that makes up the object. You must do both of these at the exact same time. You must not forget to visualize(visually) while you are doing tactile visualization, and vice versa. Forgetting to do both is to be considered a break in mental focus.
Do not continue until you can do this for at least 5 minutes with less than 3 breaks in focus.