[R-sig-Geo] overlay point extraction of pixel radius (3x3 window)

[zack holden]

Dear list,
 
I would like to use points to extract values from underlying grids, modifying my query to return the mean, standard deviation, or other function of the cells adjacent to the center grid cell. I assume this is possible, but I can find no examples of this in previous posts or in the Bivand et al. Applied spatial data analysis book. 
 
Would anyone be willing to suggest how to do this or better yet, provide some example code? 
 
Thanks in advance for any help,
 
Zack