Answer
$H_0:M_D=0$ versus $M_D\lt0$
Work Step by Step
$H_0:$ the simple stimulus has the same reaction time than the go/no-go stimulus.
$H_1:$ the simple stimulus has a lower reaction time than the go/no-go stimulus.
Let the "simple" values to be the X and the "go/no-go" values to be the Y.
And $D_i=X_i-Y_i$
