Brain Imaging & Analysis Center

usage: eyecalproc ProcFlag [smoothms scr_wid scr_hgt NstDevs DetrendNodes]

The EyeCalProc command lets you preprocess, calibrate, and/or display eye data. This command assumes that eye-tracking data has already been loaded into the following memory variables:

• eyetimes - array of eye-position time points
• eyevals - matrix of eye-position locations
• eye_affine - affine transormation calibration matrix (if PROCFLAG 16)
• eyescrwid - integer screen width during calibration (if PROCFLAG 32)
• eyescrhgt - integer screen height during calibration (if PROCFLAG 64)

These data values could have been loaded using the Eyecalwks command, or the Eyecalib command.

The first argument (PROCFLAG) controls what the command should do. The PROCFLAG options are (combine by adding):

  1 - remove spikes (greater than NSTDEVS from the mean)
  2 - remove X drifts
  4 - remove Y drifts
  8 - smooth values
 16 - apply calibration transform
 32 - normalize X values to screen center
 64 - normalize X values to screen center
128 - keep spikes only (for testing)

If multiple processing options are selected, they will be performed in the following order:

 Spikes -> Drifts -> Normalizing -> Smoothing -> Calibration

The SMOOTHMS option specifies the temporal smoothing time constant (default = 500ms).

The SCR_WID and SCR_HGT arguments let you explicitly specify the screen width and height (in pixels) when the calibration was performed. This is only used if PROCFLAG has its 32 or 64 bits set.

NSTDEVS is the number of standard deviations from the mean that should be used to define a spike signal (default = 5). This is only used if PROCFLAG has its 1 bit set.

DETRENDNODES is the number of temporal nodes to use when calculating signal drifts (default = 20). This is only used if PROCFLAG has its 2 or 4 bits set. If so, CIGAL's DETREND macro program will be used to calculate the mean signal at DETRENDNODES time points, interpolate a smooth spline curve through those points, and then subtract that low frequency drift signal from the eye position signal.

The results of EYECALPROC processing are stored in the same EYETIMES and EYEVALS data variables that it started with.

See Also:
Eyetracking, Eyetracker hardware, Eyecalib, Eyecalmap, Eyecalwks.

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