threshold about sliceviewer

 Hi,  expert 
I have used the rest_sliceviewer to show the results after t test. My t test is uncorrected p value=0.05, voxel size=10, and the corresponding t value=1.69. So, I input the t value 1.69 into the threshold text in the slice viewer, but there is nothing left, no any activation area in the slice viewer. If  I change the threshold to less than 0.2, then there are some activation area. So, I am not sure what the threshold in the rest_sliceviewer exactly mean to.  And how to explain the above phenomenon.  I will be looking forward to your kind reply. Many thanks!
Best regards,
frog