Your circuit diagram is not clear. I am not able to tell if it is p-MOS or n-MOS. However, it is not difficult at all. Just do the following: if it is a p-MOS, then it turns on when the gate voltage is lower (at logic 0). If it is an n-MOS, it turns on when the gate voltage is higher (at logic 1). I assume these are enhancement type of MOSFET.