[en] Role of turbulence spreading in edge-core coupling is studied using a simple analytic model of turbulent eddy evolution and newly developed gyrokinetic simulation capabilities including the mean E x B shear and non-circular cross section. We perform a series of numerical experiments by placing an E_γ well, with varying strength, next to the region where the ITG instability is linearly unstable. It is found that an E x B shear layer with an experimentally relevant level of the shearing rate can significantly reduce the spreading extent and speed of the propagation. From the spatio-temporal evolution of the turbulence propagation front, we find that the spreading slows down significantly in the region of higher shearing rate, rather than at the bottom of the E_γ well. Therefore, the E x B shearing rate, ω_E, is the key local quantity in slowing down the turbulence spreading. Implications of these findings to the fast core confinement improvement after H-mode transition will be discussed. (author)