PDLI is a measure of constancy over trials of the difference in phase angle between two channels, as a function of frequency and of time relative to the start of the stimulus for each trial. The range of PDLI is from zero to 1.0, with high values at a time and frequency indicating little variation, among trials, of phase angle difference between channels of the pair, at that time and frequency. PDLI is defined for frequency f at time t as: PDLI(t,f)=|〈cos(ϕA(t,f)−ϕB(t,f))〉+i〈sin(ϕA(t,f)−ϕB(t,f))〉|where ϕA and ϕB are phase angles of channels A and B, respectively. This definition of PDLI is equivalent to a definition of PLV, phase lock value, in Brunner et al. (2005). By means of some standard trigonometric identities the equation above is equivalent to the following, which, as for PLI, does not require that the phase angles be calculated: PDLI(t,f)=|〈cosϕA(t,f)cosϕB(t,f)+sinϕA(t,f)sinϕB(t,f)〉+i〈sinϕA(t,f)cosϕB(t,f)−cosϕA(t,f)sinϕB(t,f)〉|.
