What data is it that you want to transfer? I've used Processing with Matlab a few times and arrays transfer well if you write them to a file. If you want to it is possible to call Processing libraries from Matlab directly and use Processing data types too but I haven't got the example code here, I only use it at work.

I worked on a project a while back and I did the opposite: I performed calculations in MATLAB, output the values as csv files, which I then parsed and read in Processing 1.5.1. You should be able to work the other way round. MATLAB is well geared for up for reading and parsing various file formats: there is plenty of advice on the MATLAB site and forum with regard to parsing files, including csvread, or fscanf. Hope this helps.