SEPARATING SPATIALLY DISTRIBUTED RESPONSE TO STIMULATION FROM BACKGROUND .1. OPTICAL IMAGING

We consider the problem of estimating a small stimulus-induced respons e to stimulation that is masked by a fluctuating background when measu rements of the background in the absence of stimulation are available, as is common in optical imaging of the cortex and in many other exper imental situations. Two related methods based on the Karhunen-Lohe pro cedure are discussed. One seeks the function, an indicator function, t hat is most parallel to the response data and most orthogonal to the b ackground data. The second removes the subspace spanned by the backgro und from the response. Numerical investigations on simulated optical i maging data show that the first method is generally superior. Connecti ons between the two methods and techniques for assessing the quality o f the result are discussed.