Using simultaneous observations in X-rays and optical , we have performed a homogeneous analysis of the cross-correlation behaviours of four X-ray binaries : SWIFT J1753.5 - 0127 , GX 339 - 4 , Sco X-1 , and Cyg X-2 .
With high time-resolution observations using ULTRACAM and RXTE , we concentrate on the short time-scale , \delta t < 20 s , variability in these sources .
Here we present our database of observations , with three simultaneous energy bands in both the optical and the X-ray , and multiple epochs of observation for each source , all with \sim second or better time resolution .
For the first time , we include a dynamical cross-correlation analysis , i.e. , an investigation of how the cross-correlation function changes within an observation .
We describe a number of trends which emerge .
We include the full dataset of results , and pick a few striking relationships from among them for further discussion .

We find , that the surprising form of X-ray/optical cross-correlation functions , a positive correlation signal preceded by an anti-correlation signal , is seen in all the sources at least some of the time .
Such behaviour suggests a mechanism other than reprocessing as being the dominant driver of the short-term variability in the optical emission .
This behaviour appears more pronounced when the X-ray spectrum is hard .
Furthermore , we find that the cross-correlation relationships themselves are not stable in time , but vary significantly in strength and form .
This all hints at dynamic interactions between the emitting components which could be modelled through non-linear or differential relationships .