The Wide Field Infrared Survey Telescope (WFIRST) is an upcoming NASA observatory that will investigate the origins of cosmic acceleration using weak gravitational lensing. WFIRST will perform galaxy shape measurements using Teledyne H4RG-10 detectors; thus it is essential to understand inter-pixel non-linearities like the brighter-fatter effect (BFE) and non-linear inter-pixel capacitance (NL-IPC) that could cause systematic errors in the lensing analysis. The non-destructive readout capability of the H4RG-10 detectors enables correlation measurements on flat field data not only between pixels but also between time frames. In this talk, I will present a correlation analysis of flat field data (obtained from the Detector Characterization Laboratory) for one of the WFIRST prototype detectors. After correcting for classical non-linearity, we find a statistically significant residual correlation signal. We leverage the time dimension of this data set to perform some tests that suggest that the BFE is the dominant mechanism. The flat field statistics continue to provide a wealth of information that will eventually help us calibrate WFIRST data and obtain accurate cosmological parameters.