Simple slopes tests for 4-way, mixed regression interaction - Please help!

I have conducted a regression analysis that yields a significant 4-way interaction between:
2 dichotomous within-subjects variables
2 continuous variables
(also controlling for a number of other variables)

Any advice on how to unpack this result in R or SPSS?

Here is a little more info if needed:
I'm looking at people's response times on a task. They are exposed to one of two types of images (dichotomous variable 1) and then shown one of two types of words (dichotomous variable 2) before they respond. The two continuous variables are individual difference measures, and we are controlling for things like age and gender. In regards to our research question, it makes the most sense to look at differences in behavior within the 4 quadrants of the individual difference measures (low/low, low/high, high/low, high/high).