Dependency of cross-correlation on signal/noise ratio and independence from uniform cortical activation in the absence of overlying noise. Zero-lag cross correlation obtained between the reference site shown in figure 1, and another site located at the point of mirror-image symmetry, adjacent to the right hand input site. Mean and SEM of cross-correlations from 20 1s simulation runs. In addition to the twin sites of asynchronous noise input to the same driving sites as in figure 1, spatio-temporally white noise has been input to all other sites in the field. The noise-to-signal ratio refers to the ratio of rms amplitude of the random field noise, to that at the twin ``driving'' sites. Results are shown for two widely different conditions of non-specific cortical activation, as indicated by the value of parameter Qns.