nbasis: Return number of basis functions associated with HRF

In bbuchsbaum/fmrireg: R package for the anlysis of fmri data

Return number of basis functions associated with HRF

Description

Get the number of basis functions used in a hemodynamic response function (HRF) or model term. For canonical HRFs (like SPM's canonical HRF), this returns 1. For flexible basis sets (like Fourier or B-spline bases), this returns the number of basis functions used to model the response shape.

Usage

nbasis(x)

## S3 method for class 'convolved_term'
nbasis(x)

## S3 method for class 'hrfspec'
nbasis(x)

Arguments

x	The object to query (typically an HRF, hrfspec, or convolved_term)

Value

An integer indicating the number of basis functions:

• 1 for canonical HRFs (e.g., SPM gamma)

• >1 for flexible basis sets (e.g., Fourier, B-spline)

• For convolved terms: number of basis functions per condition

See Also

HRF_SPMG1(), event_model()

Other hrf: fitted_hrf()

Examples

# Check basis functions for different HRF types

# Canonical HRF (single basis)
canonical_hrf <- HRF_SPMG1
nbasis(canonical_hrf)  # Returns: 1

# Fourier basis set
fourier_hrf <- getHRF("fourier", nbasis = 3)
nbasis(fourier_hrf)  # Returns: 3

# Create event model with multiple basis functions
event_data <- data.frame(
  condition = factor(c("A", "B", "A", "B")),
  onsets = c(1, 10, 20, 30),
  run = c(1, 1, 1, 1)
)
sframe <- sampling_frame(blocklens = 50, TR = 2)

# Model with Fourier basis
evmodel <- event_model(
  onsets ~ hrf(condition, basis = "fourier", nbasis = 3),
  data = event_data,
  block = ~run,
  sampling_frame = sframe
)

# Get number of basis functions for model term
nbasis(evmodel)  # Returns: 3 (basis functions per condition)

bbuchsbaum/fmrireg documentation built on March 1, 2025, 11:20 a.m.