Click on the Quick Mask mode button in the Photoshop toolbox. This will
create a Quick Mask channel in the Channels palette.

Choose the Rectangular Marquee tool in the Photoshop toolbox.
Select an area in the center of the image.

Choose Fill... from the Edit menu. Fill the selection area with black
at 100% opacity.

Choose None from the Select menu to deselect the area. Then choose
Gaussian Blur... from the Blur submenu in the Filter menu. Use a Radius setting of between 10 and 20 pixels. You have now applied the Gaussian Blur to the Quick Mask channel.

Select a special effects filter from the Filter menu. In this example, I used
the Sprayed Strokes. Since you are still in Quick Mask mode and there is nothing selected, only the Quick Mask channel will be effected by the filter.

Click on the Standard selection mode button in the Photoshop toolbox.
This will select the area of the image that is not masked by the Quick Mask channel. Fill the area with your background color, and your done.