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Fit a Robust Linear Model for fMRI Data Analysis

Source: R/fmrirlm.R
fmri_rlm.Rd

This function fits a robust linear regression model for fMRI data analysis using the specified model formula, block structure, and dataset. The model can be fit using either a runwise or chunkwise data splitting strategy.

Usage

fmri_rlm(
  formula,
  block,
  baseline_model = NULL,
  dataset,
  durations = 0,
  drop_empty = TRUE,
  strategy = c("runwise", "chunkwise"),
  nchunks = 10,
  cor_struct = c("iid", "ar1", "ar2", "arp"),
  cor_iter = 1L,
  cor_global = FALSE,
  ar_p = NULL,
  ar1_exact_first = FALSE,
  robust_psi = c("huber", "bisquare"),
  robust_k_huber = 1.345,
  robust_c_tukey = 4.685,
  robust_max_iter = 2L,
  robust_scale_scope = c("run", "global", "voxel"),
  ...
)

Arguments

formula

A model formula describing the event structure or an fmri_model object.

block

Formula describing run/block structure.

baseline_model

Optional baseline/nuisance model.

dataset

An fmri_dataset. For an fmri_model method this may be omitted when the model already owns its dataset.

durations

Event durations passed to model construction.

drop_empty

Remove empty factor levels during model construction.

strategy

Fit runs separately and combine them, or fit a joint model partitioned into voxel chunks.

nchunks

Number of data chunks when strategy is "chunkwise". Default is 10.

cor_struct

Correlation structure: "iid", "ar1", "ar2", or "arp". Default is "iid".

cor_iter

Number of iterations for AR parameter estimation. Default is 1.

cor_global

Whether to use global AR parameters. Default is FALSE.

ar_p

Order of autoregressive model for "arp" structure. Default is NULL.

ar1_exact_first

Whether to use exact AR(1) for first iteration. Default is FALSE.

robust_psi

Robust psi function: "huber" or "bisquare". Default is "huber".

robust_k_huber

Tuning constant for Huber's psi. Default is 1.345.

robust_c_tukey

Tuning constant for Tukey's bisquare. Default is 4.685.

robust_max_iter

Maximum iterations for robust fitting. Default is 2.

robust_scale_scope

Scope for robust scale estimation: "run", "global", or "voxel". Default is "run".

...

Additional arguments passed to fmri_lm

Value

A fitted robust linear regression model for fMRI data analysis.

Examples

etab <- data.frame(onset=c(1,30,15,25), fac=factor(c("A", "B", "A", "B")), run=c(1,1,2,2))
etab2 <- data.frame(onset=c(1,30,65,75), fac=factor(c("A", "B", "A", "B")), run=c(1,1,1,1))
mat <- matrix(rnorm(100*100), 100,100)
dset <- fmridataset::matrix_dataset(mat, TR=1, run_length=c(50,50),event_table=etab)
dset2 <- fmridataset::matrix_dataset(mat, TR=1, run_length=c(100),event_table=etab2)
lm.1 <- fmri_rlm(onset ~ hrf(fac), block= ~ run, dataset=dset)
lm.2 <- fmri_rlm(onset ~ hrf(fac), block= ~ run, dataset=dset2)