fmrihrf

Hemodynamic response functions and event-related regressors for fMRI analysis in R.

fmrihrf provides a composable toolkit for constructing, modifying, and convolving HRFs with experimental designs. It ships with standard basis sets (SPM canonical, B-spline, Fourier, FIR, Gamma, Gaussian, and more), decorators for time-shifting and blocking, and a fast C++ convolution backend.

Installation

# From CRAN
install.packages("fmrihrf")

# Development version
remotes::install_github("bbuchsbaum/fmrihrf")

Quick start

library(fmrihrf)

# Evaluate the SPM canonical HRF over 0-30 seconds
t <- seq(0, 30, by = 0.1)
y <- evaluate(HRF_SPMG1, t)
plot(t, y, type = "l", xlab = "Time (s)", ylab = "Response")

# Build a regressor from event onsets
reg <- regressor(onsets = c(2, 10, 18), hrf = HRF_SPMG1,
                 duration = 0, amplitude = 1,
                 span = 24, sampling_frame = sampling_frame(blocklens = 100, TR = 1))
plot(reg)

Key features

Multiple basis sets — Use a single canonical HRF or a flexible basis set to capture response variability.

HRF_SPMG1                                    # SPM canonical (double gamma)
HRF_SPMG3                                    # canonical + temporal & dispersion derivatives
hrf_bspline(t, N = 6)                        # B-spline basis
hrf_fourier(t, N = 5)                        # Fourier basis

Decorators — Modify any HRF through functional composition.

lag_hrf(HRF_SPMG1, lag = 2)                  # shift peak by 2 s
block_hrf(HRF_SPMG1, width = 15)             # sustained/blocked response
normalise_hrf(HRF_SPMG1)                     # unit peak-normalised

Custom HRFs — Wrap any f(t) into the HRF system.

my_hrf <- as_hrf(function(t) exp(-t / 5), name = "exponential", span = 20)
evaluate(my_hrf, seq(0, 20, by = 1))

Regressor construction — Convolve events with HRFs to produce design-matrix columns, with support for variable durations, amplitudes, and multi-basis expansion.

sf <- sampling_frame(blocklens = c(200, 200), TR = 2)
reg <- regressor(onsets = c(10, 30, 50), hrf = HRF_SPMG1,
                 duration = c(0, 5, 0), amplitude = c(1, 1.5, 1),
                 sampling_frame = sf)
evaluate(reg)

Fast convolution — Core routines are implemented in C++ (Rcpp / RcppArmadillo) for efficient large-scale design matrix generation.

Documentation

Full documentation is available at https://bbuchsbaum.github.io/fmrihrf/.

Vignettes cover the main workflows:

• Hemodynamic Response Functions — overview of built-in HRFs and the basis-set system
• Building Regressors — constructing design-matrix regressors from event timing
• HRF Generators — programmatically generating families of HRFs
• Advanced Modeling and Design — multi-basis designs, trial-varying HRFs, and more

License

MIT

Albers theme

This package uses the albersdown theme. Existing vignette theme hooks are replaced so albers.css and local albers.js render consistently on CRAN and GitHub Pages. The palette family is provided via params$family (default ‘red’). The pkgdown site uses template: { package: albersdown }.