Phase Encoding Analysis (Matlab)

In phase-encoded retinotopic mapping stimulation is periodic, allowing polar angle (rotating wedge) and eccentricity (expanding / contracting ring) to be encoded in the phase of the BOLD signal observed in each voxel. This phase can be extracted in a number of ways (e.g. cross-correlation). In the PEA tool provided in the CNI toolbox, the phase is extracted by using a cosine and sine wave at the stimulation frequency as predictors in a linear regression. This allows not only to extract phase and amplitude of of each voxel's response from the fit beta coefficients, but also to obtain an F-statistic and p-value to assess statistical significance.