hpf
The frequency at which to apply a highpass filter to the data
during pre-processing, in Hertz. Default: 0
Hz (disabled). If the
data has not already been highpass filtered, a recommended filter value is
.01
Hz.
The highpass filter serves to detrend the data, since low-frequency
variance is associated with noise. Highpass filtering is accomplished by
nuisance regression of discrete cosine transform (DCT) bases.
Note the TR
argument is required for highpass filtering. If
TR
is not provided, hpf
will be ignored.