[R] Repost: Estimation when interaction is present: How do I get get the parameters from nlme?

Gday, This is a repost since I only had one direct reply and I remain mystified- This may be stupidity on my part but it may not be so simple. In brief, my problem is I'm not sure how to extract parameter values/effect sizes from a nonlinear regression model with a significant interaction

[R] interaction terms in regression analysis

object for a specific combination of factors including the interaction term. i.e. what is the ed50 (and std err) for A-/B-, A+/B-, A-/B+, A+/B+ ? Regards John S. Walker, PhD Department of Physiology Biophysics University of Illinois at Chicago 835 Sth Wolcott Ave MC 901 Chicago IL 60612 USA