How do I script trackMatte Properties?

Hello Dan

How do I script the trackmatte ?

AlphaMatte

AlphaInvertMatte

LumaMatte

LumainvertMatte

I have this script

for (i = 0; i < activeItem.selectedLayers.length; i++) {    // loop through selected layers in the comp

         theLayer = activeItem.selectedLayers;

           var thePreset = File("/Applications/Adobe After Effects CS5/Presets/ShiftChannel.ffx");

theLayer.applyPreset(thePreset);  // add animation preset to selected layers

               theLayer.property("Opacity").setValue(50); // set opacity to selected layer

             theLayer.property("TrackMatte").setTrackMatte(AlphaMatte); //set trackMatte to selected layer ??

Thanks

Rob