hemodynamic regressor specification function for model formulas.

This function is to be used in formulas for fitting functions, e.g. onsets ~ hrf(fac1,fac2) ... It captures the variables/expressions provided and packages them with HRF/contrast information into an hrfspec object, which is then processed by event_model.

Usage

hrf(
  ...,
  basis = "spmg1",
  onsets = NULL,
  durations = NULL,
  prefix = NULL,
  subset = NULL,
  precision = 0.3,
  nbasis = 1,
  contrasts = NULL,
  id = NULL,
  name = NULL,
  lag = 0,
  summate = TRUE
)

Arguments

...: One or more variable names (bare or character) or expressions involving variables present in the data argument of event_model.
basis: the impulse response function or the name of a pre-supplied function, one of: "gamma", "spmg1", "spmg2", "spmg3", "bspline", "gaussian", "tent", "bs". Can also be an HRF object.
onsets: optional onsets override. If missing, onsets will be taken from the LHS of the main model formula.
durations: optional durations override. If missing, durations argument from event_model is used.
prefix: a character string that is prepended to the variable names and used to identify the term. Can be used to disambiguate two hrf terms with the same variable(s) but different onsets or basis functions.
subset: an expression indicating the subset of 'onsets' to keep.
precision: sampling precision in seconds.
nbasis: number of basis functions – only used for hemodynamic response functions (e.g. bspline) that take a variable number of bases.
contrasts: one or more contrast_spec objects created with the contrast, pair_contrast etc. functions. Must be NULL, a single contrast spec, or a named list of contrast specs.
id: a unique character identifier used to refer to term, otherwise will be determined from variable names.
name: Optional human-readable name for the term.
lag: a temporal offset in seconds which is added to onset before convolution
summate: whether impulse amplitudes sum up when duration is greater than 0.

Value

an hrfspec instance

Examples


## 'hrf' is typically used in the context of \code{formula}s passed to `event_model`.

# Simple model with one factor
form1 <- onsets ~ hrf(condition, basis="spmg1")

# Model with factor and continuous modulator, using default SPMG1 for both terms
form2 <- onsets ~ hrf(condition) + hrf(RT)

# Model with interaction term and SPMG3 basis
form3 <- onsets ~ hrf(condition, RT, basis="spmg3")

# Model with an expression and contrasts
library(rlang)
con1 <- pair_contrast(~ condition == "A", ~ condition == "B", name="AvB")
form4 <- onsets ~ hrf(condition, Poly(RT, 2), contrasts=con1)