Try one of these options -
gauss = 2*(gauss-0.5); %%// For a range of [-1 1];
imagesc( gauss, [-1 1] );
Or
gauss = gauss/2; %%// For a range of [0 0.5];
imagesc( gauss, [0 0.5] );
Or
gauss = 0.5*(gauss-1); %%// For a range of [-0.5 0];
imagesc( gauss, [-0.5 0] );