In the image there is term called (1/g)and term and sigma(t). Both attenuating the signal,but i cannot understand the difference between them. Thank you

 

First the symbol that sigma(t) is connected to is that of an adder, (circle with a "+" in it) not a multiplier, so X(t)/G gets added to sigma(t), just like the output equation says. Secondly it looks like the author forgot to put in the multiplication symbol for the 1/G label, which could be a circle with an "X" in it.