I would suggest you start with 5-10 mg doses taken orally. Edibles are going to be the easiest way to know how much you're consuming. You may very well need more based on your existence tolerance, body size, etc, but be advised that edibles generally take a very long time (60-120 minutes) to kick in. I don't consume cannabis often, but I notice that when I do, I tend to stutter more often because I'm less conscious about using techniques that increase the fluidity of my speech (pacing, releasing the tension in my mouth, etc.). Good luck with the study!