| CROSSF | Returns estimates and plot of event-related coherence (ERC) changes between data from two input channels. The lower panel gives the coherent phase difference between the processes. In this panel, for Ex. -90 degrees (blue) means xdata leads ydata by a quarter cycle. 90 degrees (orange) means ydata leads xdata by a quarter cycle. Click on each subplot to view separately and zoom in/out. |
| Function description: | Uses EITHER fixed-window, zero-padded FFTs (faster) OR constant-Q 0-padded DFTs (better sensitivity), both Hanning-tapered. Output frequency spacing is the lowest frequency (srate/winsize) divided by the padratio. If 'alpha' is given, then bootstrap statistics are computed (from a distribution of 200 (g.naccu) surrogate baseline data epochs) for the baseline epoch, and non-significant features of the output plots are zeroed (e.g., plotted in green). Baseline epoch is all windows with center times < 'baseline' or the whole epoch if 'baseboot' is set to 1. |
| Usage: | >> [coh,mcoh,timesout,freqsout,cohboot,cohangles] = crossf(xdata,ydata, frames,tlimits,titl, srate,cycles,winsize,timesout, padratio,maxfreq,alpha,verts); |
| Inputs: | |
xdata |
first single-channel (1,frames*nepochs) data {none} |
ydata |
second single-channel (1,frames*nepochs) data {none} |
frames |
frames per epoch {768} |
tlimits |
[mintime maxtime] (ms) epoch time limits {[-1000 2000]} |
srate |
data sampling rate (Hz) {256} |
cycles |
>0 -> Number of cycles in each analysis wavelet =0 -> Use FFTs (with constant window length) {0} |
| Optional crossf type: | |
'type' |
['coher'|'phasecoher'], compute either the coherence ('coher') or the phase coherence ('phasecoher') also known as the phase coupling factor of the two data inputs. Default is 'phasecoher' { 'phasecoher' }. |
| Optional Detrend: | |
'detret' |
['on'|'off'], Detrend data in time. {'off'} |
'detrep' |
['on'|'off'], Detrend data across epochs (trials) {'off'} |
| Optional FFT/DFT: | |
'winsize' |
If cycles==0: data subwindow length (fastest, 2^n |
'timesout' |
Number of output times (int |
'padratio' |
FFT-length/winframes (2^k) {2} Multiplies the number of output frequencies by dividing their spacing. When cycles==0, frequency spacing is (low freq/padratio). |
'maxfreq' |
Maximum frequency (Hz) to plot (& output if cycles>0) {50} If cycles==0, all FFT frequencies are output. |
'baseline' |
ERSP baseline end time (ms). {0} |
'powbase' |
Baseline spectrum to log-subtract. {def|NaN->from data} |
| Optional Bootstrap: | |
'alpha' |
If non-0, compute Two-tailed bootstrap significance prob. level. Show non-signif output values as green. {0} |
'naccu' |
Number of bootstrap replications to compute {200} |
'baseboot' |
Bootstrap baseline subtract (0=same as 'baseline'; 1=whole epoch) {0} |
'topovec' |
Scalp topography (map) to plot {[]} |
'elocs' |
Electrode location file for scalp map {no default} File should be ascii in format of >> topoplot example |
| Optional Plot: | |
'plotamps' |
['on'|'off'], Plot amplitude {'on'} |
'plotphase' |
['on'|'off'], Plot phase {'off'} |
'title' |
Optional figure title {none} |
'marktimes' |
Times to mark with a dotted vertical line{def|NaN->none} |
'linewidth' |
Line width for marktimes traces (thick=2, thin=1) {2} |
'cmax' |
maximum amplitude for color scale { use data limits } |
'angleunit' |
angle plotting units 'ms' for milliseconds or 'deg' for degree of angle { 'deg' } |
'pboot' |
Bootstrap power limits (from timefm data} |
'rboot' |
Bootstrap ITC limits (from timef) {def|NaN->from data} |
'axesfont' |
Font size for the axes {10} |
'titlefont' |
Font size for the title {8} |
| Outputs: | |
coh |
between-channel coherency changes (nfreqs,timesout) |
mcoh |
vector of mean baseline coherence at each frequency |
timesout |
vector of output times (subwindow centers) in ms. |
freqsout |
vector of frequency bin centers in Hz. |
cohboot |
[2,nfreqs] matrix of [lower;upper] coh significance diffs. |
cohangle |
coherency angles (nfreqs,timesout) |
| Note: | when cycles==0, nfreqs is total number of FFT frequencies. |
| Authors: | Sigurd Enghoff, Scott Makeig & Arnaud Delorme SCCN/INC/UCSD, La Jolla, 1998-2002 |
| See also: | timef |