How can I change the speech rate while text-to-speech is going on? Is it possible to do that? I currently activate the text-to-speech feature by hitting CMD+SHIFT+S. However, while reading textbooks, I sometimes need to go slower to increase understanding, or pause. How do I achieve that?

Thanks!
Go into system preferences and into speech, then select the tab "Text to speech" the second option down is speaking rate, adjust the slider :)