B-spline HRF (hemodynamic response function)

The `hrf_bspline` function computes a B-spline basis for an HRF at time points `t`. The `N` basis functions are the interior functions of a clamped B-spline basis on [0, span] with evenly spaced knots: the functions anchored at the two boundaries are dropped, so every basis function (and therefore every fitted HRF) is zero at onset and at the end of the span. Outside [0, span] the basis is zero.

Usage

hrf_bspline(t, span = 24, N = 5, degree = 3, ...)

Arguments

t

A vector of time points.

span

A numeric value representing the temporal window over which the basis set spans. Default value is 24.

N

An integer representing the number of basis functions. Must be at least degree - 1. Default value is 5.

degree

An integer representing the degree of the spline. Default value is 3.

...

Further arguments passed to bs (intercept, df and knots are set internally and ignored if supplied).

Value

A matrix representing the B-spline basis for the HRF at the given time points `t`.

See also

Other hrf_functions: hrf_basis_lwu(), hrf_boxcar(), hrf_gamma(), hrf_gaussian(), hrf_inv_logit(), hrf_lwu(), hrf_mexhat(), hrf_sine(), hrf_spmg1(), hrf_time(), hrf_weighted()

Examples

# Compute the B-spline HRF representation for time points from 0 to 20 with 0.5 increments
hrfb <- hrf_bspline(seq(0, 20, by = .5), N = 4, degree = 2)