Tools -> Tablet...
PhotoSEAM has support for pressure sensitive tablets. This gives you not only better control over the stroke, but also it allows you to control the opacity or density of the brush. In cases of Art brushes it really gives the impression of painted stroke.
To set up the pressure support open the Tablet properties from menu Tools.
Each brush can handle the pressure differently. There is an option in the Brush Properties for that.
Example of few Artistic brushes using pressure sensitivity.
Airbrush can be also controlled with pressure very well.
The pressure sensitive stylus has in many cases (for example Wacom series) an "eraser" on the top of it. When you turn your stylus and use it as an eraser you will:
Try It! It is very convenient!
Note: When you are using the stylus to draw and then you switch to mouse, the first stroke with mouse will be "silent" . This is needed in order to properly reset the tool.